Apportionment and Redistricting Process for the U.S. House of Representatives

Apportionment and Redistricting Process for
May 12, 2021
the U.S. House of Representatives
Sarah J. Eckman
The census, apportionment, and redistricting are interrelated activities that affect representation
Analyst in American
in the U.S. House of Representatives. Congressional apportionment (or reapportionment) is the
National Government
process of dividing seats for the House among the 50 states following the decennial census.

Redistricting refers to the process that follows, in which states create new congressional districts
or redraw existing district boundaries to adjust for population changes and/or changes in the

number of House seats for the state. At times, Congress has passed or considered legislation
addressing apportionment and redistricting processes under its broad authority to make law affecting House electio ns under
Article I, Section 4, of the U.S. Constitution. These processes are all rooted in provisions in Article I, Section 2 (as amen ded
by Section 2 of the Fourteenth Amendment).
Seats for the House of Representatives are constitutionally required to be divided among the states, based on the population
size of each state. To determine how many Representatives each state is entitled to, the Constitution requires the national
population to be counted every 10 years, which is done through the census. The Con stitution also limits the number of
Representatives to no more than one for every 30,000 persons, provided that each state receives at least one Representative.
Additional parameters for the census and for apportionment have been established through federal statutes, including
timelines for these processes; the number of seats in the House; and the method by which House seats are divided among
states. Congress began creating more permanent legislation by the early 20th century to provide recurring procedures for the
census and apportionment, rather than passing measures each decade to address an upcoming reapportionment cycle. Federal
law related to the census process is found in Title 13 of the U.S. Code, and two key statutes affecting apportionment today are
the Permanent Apportionment Act of 1929 and the Apportionment Act of 1941.
April 1 of a year ending in “0” marks the decennial census date and the start of the apportionment population counting
process; the Secretary of Commerce is to report the apportionment population of each state to the President by the end of that
year. Within the first week of the first regular session of the next Congress, the President is to transmit a statement to the
House relaying state population information and the number o f Representatives each state is entitled to. For a discussion of
recent changes to this timeline, see CRS Insight IN11360, Apportionment and Redistricting Following the 2020 Census. Each
state receives one Representative, as constitutionally required, and the remaining seats are distributed using a mathematical
approach known as the method of equal proportions, established by the Apportionment Act of 1941. Essentially, a ranked
“priority list” is created indicating which states receive the 51st-435th House seats, based on a calculation involving each
state’s population size and the number of additional seats a state has received. The U.S. apportionment population from the
2020 census was 331,108,434, reflecting a 7.1% increase since 2010, and 7 House seats were reapportioned among 13 states.
After a census and apportionment are completed, state officials receive updated population information from the U.S. Census
Bureau and the state’s allocation of House seats from the Clerk of the House. Single-member House districts are required by
2 U.S.C. §2c, and certain other redistricting standards, largely related to the composition of districts, have been established by
federal statute and various legal decisions. Current federal parameters related to redistricting criteria generally address
population equality and protections against discrimination for racial and language minority groups under the Voting Rights
Act of 1965 (VRA), as amended. Previous federal apportionment statutes have, at times, included other district criteria, such
as geographic compactness or contiguity, and these standards have sometimes been referred to in U.S. Supreme Court cases,
but they are not included in the current federal statutes that address the apportionment process. These redistricting principles
and others, such as considering existing political boundaries, preserving communities of interest, and promoting political
competition, have been commonly used across states, and many are reflected in state laws today.
The procedural elements of redistricting are generally governed by state laws, and state redistricting practices can vary
regarding the methods used for drawing districts, timeline for redistricting, and which actors (e.g., elected officials,
designated redistricting commissioners, and/or members of the public) are involved in the process. Mapmakers must often
make trade-offs between one redistricting consideration and others, and making these trade-offs can add an additional
challenge to an already complicated task of ensuring “fair” representation for district residents. Despite technological
advances that make it easier to design districts with increasing geographic and demographic precision, the overall task of
redistricting remains complex and, in many instances, can be controversial. A majority of states, for example, faced legal
challenges to congressional district maps drawn following the 2010 census, and these legal challenges can take multiple years
to resolve.
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Contents
Introduction ................................................................................................................... 1
Apportionment Process .................................................................................................... 1

Federal Requirements/Guidelines for Reapportionment: History and Current Policy ............ 4
Reapportionment Method and Timeline......................................................................... 5
Redistricting Process ....................................................................................................... 7
Federal Requirements/Guidelines for Redistricting: History and Current Policy .................. 8
Population Equality .............................................................................................. 9
Racial/Language Minority Protections ................................................................... 11
Other Redistricting Considerations ............................................................................. 11
Compactness and Contiguity ................................................................................ 13
Preserving Political Subdivisions .......................................................................... 13
Preserving Communities of Interest....................................................................... 14
Promoting Political Competition; Considering Existing District or Incumbent ............. 14

State Processes for Redistricting ................................................................................ 14
Congressional Options Regarding Redistricting............................................................ 17
Concluding Observations ............................................................................................... 17

Figures
Figure 1. Typical Timeline of Census, Apportionment, and Redistricting Process ...................... 1
Figure 2. Changes to Average District Apportionment Population Sizes and House Seats
Over Last Four Apportionment Cycles, 1990-2020 ............................................................ 4
Figure 3. State Redistricting Methods............................................................................... 15

Tables
Table 1. Loss or Gain of U.S. House Seats in States Following 2020 Census ............................ 3
Table 2. Scope of Apportionment Changes, 1910-2020 ......................................................... 3
Table 3. Summary of Average U.S. House District Population Sizes, 1910-2020 ..................... 10
Table 4. Selected Congressional Redistricting Criteria Specified by Certain States .................. 11

Table A-1. Hamilton/Vinton Method—Sample Apportionment ............................................. 21
Table A-2. Jefferson Method—Sample Apportionment........................................................ 22
Table A-3. Webster Method—Sample Apportionment ......................................................... 23
Table A-4. Huntington-Hill Method—Sample Apportionment .............................................. 24
Table A-5. Sample Priority Values and Resulting Priority List for Selected Values................... 25

Appendixes
Appendix. Determining an Apportionment Method ............................................................ 19

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Contacts
Author Information ....................................................................................................... 25

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Apportionment and Redistricting Process for the U.S. House of Representatives

Introduction
Every 10 years, the U.S. population is counted through the national census, and districts for the
U.S. House of Representatives are readjusted to reflect the new population level and its
distribution across states through the federal apportionment and state redistricting processes. The
requirement to have proportional representation in the House is found in the U.S. Constitution,
and constitutional provisions also underlie other elements of the census, apportionment, and
redistricting practices. Figure 1 provides a generalized timeline for how these three interrelated
processes occur, and the sections of the report that follow provide additional information on
apportionment and redistricting. For a discussion of how the Coronavirus Disease 2019 (COVID-
19) pandemic affected the timing of the most recent census and apportionment, see CRS Insight
IN11360, Apportionment and Redistricting Following the 2020 Census. For additional
information on the census process, see CRS Report R44788, The Decennial Census: Issues for
2020, and CRS In Focus IF11015, The 2020 Decennial Census: Overview and Issues.
Figure 1. Typical Timeline of Census, Apportionment, and Redistricting Process

Source: CRS compilation, based on information from the U.S. Constitution, U.S. Code, U.S. Census Bureau, and
state laws. Graphic created by Amber Hope Wilhelm, CRS Visual Information Specialist.
Apportionment Process
Apportionment (or reapportionment) refers to the process of dividing seats in the U.S. House of
Representatives among the states. Article 1, Section 2, of the U.S. Constitution, as amended by
Section 2 of the Fourteenth Amendment, requires that seats for Representatives are divided
among states, based on the population size of each state. House seats today are real ocated due to
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changes in state populations, since the number of U.S. states (50) has remained constant since
1959; in earlier eras, the addition of new states would also affect the reapportionment process, as
each state is constitutional y required to receive at least one House seat.
The 2020 census reported a 7.1% overal increase in the U.S. apportionment population since the
2010 census, to 331,108,434 individuals.1 The ideal (or average) district population size increased
across most states fol owing the 2020 census, and some states experienced larger growth levels
than others.2 Three states experienced decreases in average district population size following the
2020 census.3 The average congressional district population for the United States following the
2020 census was 761,169 individuals.4 Seven U.S. House seats shifted across states following the
2020 census; seven states lost seats and six states gained seats, distributed as shown in Table 1.
Table 2 provides additional historical data on the number of states and number of seats affected
by each apportionment since 1910.
The map in Figure 2 il ustrates changes in states’ ideal district size and changes in the number of
House seats al ocated to each state between the 1990 and 2020 apportionments. Regional patterns
of population change observed following previous censuses continued in 2020, as the percentage
of House seats distributed across the Northeast and Midwest regions decreased, and the
percentage of House seats distributed across the South and West regions increased.5 California
had the largest House delegation following the 2020 census, with 52 seats; Alaska, Delaware,
North Dakota, South Dakota, Vermont, and Wyoming each had a single House seat.6

1 T he apportionment population reflects the total resident population in each of the 50 states, including minors,
noncitizens, Armed Forces personnel/dependents living overseas, and federal civilian employees/dependents living
overseas; for more information see U.S. Census Bureau, “ Congressional Apportionment: Frequently Asked Questions,”
January 8, 2021, at https://www.census.gov/topics/public-sector/congressional-apport ionment/about/faqs.html. For
2020 census results, see U.S. Census Bureau, “T able A. Apportionment Population, Resident Population, and Overseas
Population: 2020 Census and 2010 Census,” 2020 Census Apportionment Results, April 26, 2021, at
https://www2.census.gov/programs-surveys/decennial/2020/data/apportionment/apportionment-2020-tableA.xlsx
2 Colorado had the smallest increase in average district population size after the 2020 census, increasing by 2,067
individuals on average per district when compared to the 2010 census. West Virginia had the largest increase in
average district population size after the 2020 census, increasing by 277,585 individuals on average per district when
compared to the 2010 census. CRS calculations based on information provided in U.S. Census Bureau, Historical
Apportionm ent Data (1910-2020)
, April 26, 2021, at https://www.census.gov/data/tables/time-series/dec/
apportionment -data-text.html.
3 Montana’s average district population size decreased by 451,712 individuals, Oregon’s average district population
size decreased by 62,804 individuals, and Mississippi’s average district population size decreased by 3,581 individuals
after the 2020 census. CRS calculations based on information provided in U.S. Census Bureau, Historical
Apportionm ent Data (1910-2020)
, April 26, 2021, at https://www.census.gov/data/tables/time-series/dec/
apportionment -data-text.html.
4 U.S. Census Bureau, Historical Apportionment Data (1910-2020), at https://www.census.gov/data/tables/time-series/
dec/apportionment-data-text.html. See Table 3 for further information on average congressional district sizes since
1910.
5 See U.S. Census, “Presentation: 2020 Census Apportionment News Conference,” 2020 Census Apportionment Counts
Press Kit
, April 26, 2021, at https://www.census.gov/content/dam/Census/newsroom/press-kits/2021/20210426-
apportionment -presentation.pdf; see also Paul Mackun and Steven Wilson, Population Distribution and Change:
2000:2010
, U.S. Census Bureau, Report Number C2010BR-01, Washington, DC, March 2011, at
https://www.census.gov/prod/cen2010/briefs/c2010br-01.pdf; and Kristen D. Burnett, Congressional Apportionm ent:
2010 Census Briefs
, U.S. Census Bureau, Report Number C2010BR-08, Washington, DC, November 2011, pp. 4 -5, at
https://www.census.gov/content/dam/Census/library/publications/2011/dec/c2010br-08.pdf. Historical information
dating back to 1910 on state seat gains and losses, as well as the average number of people per representative in each
state, is available from U.S. Census Bureau, Historical Apportionm ent Data (1910-2020), April 26, 2021, at
https://www.census.gov/data/tables/time-series/dec/apportionment -data-text.html.
6 U.S. Census Bureau, “T able 1. Apportionment Population and Number of Representatives by State: 2020 Census,”
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Table 1. Loss or Gain of U.S. House Seats in States Following 2020 Census
Lost U.S. House Seats
Gained U.S. House Seats
State
Seat Change
State
Seat Change
California
-1
Colorado
+1
Il inois
-1
Florida
+1
Michigan
-1
Montana
+1
New York
-1
North Carolina
+1
Ohio
-1
Oregon
+1
Pennsylvania
-1
Texas
+2
West Virginia
-1


Source: U.S. Census Bureau, “Table D1. Number of Seats Gained and Lost in U.S. House of Representatives by
State: 2020 Census,” 2020 Census Apportionment Results, April 26, 2021, at https://www2.census.gov/programs-
surveys/decennial/2020/data/apportionment/apportionment-2020-tableD.xlsx.
Table 2. Scope of Apportionment Changes, 1910-2020
Total States
House Seats
States Losing
States Gaining
Affected By
Affected by
Census Year
Seats
Seats
Apportionment
Apportionment
2020
7 (14.0%)
6 (12.0%)
13 (26.0%)
7 (1.6%)
2010
10 (20.0%)
8 (16.0%)
18 (36.0%)
12 (2.8%)
2000
10 (20.0%)
8 (16.0%)
18 (36.0%)
12 (2.8%)
1990
13 (26.0%)
8 (16.0%)
21 (42.0%)
19 (4.4%)
1980
10 (20.0%)
11 (22.0%)
21 (42.0%)
17 (3.9%)
1970
9 (18.0%)
5 (10.0%)
14 (28.0%)
11 (2.5%)
1960a
16 (32.0%)
10 (20.0%)
26 (52.0%)
21 (4.8%)
1950b
9 (18.8%)
7 (14.6%)
16 (33.3%)
14 (3.2%)
1940b
9 (18.8%)
7 (14.6%)
16 (33.3%)
9 (2.1%)
1930b
21 (43.8%)
13 (27.1%)
34 (70.8%)
27 (6.2%)
1920c




1910d
0 (0.0%)
25 (54.3%)
25 (54.3%)
47 (10.9%)
Source: U.S. Census Bureau, Historical Apportionment Data Map, April 26, 2021, at https://www.census.gov/
library/visualizations/interactive/historical-apportionment-data-map.html.

2020 Census Apportionm ent Results, April 26, 2021 at https://www2.census.gov/programs-surveys/decennial/2020/
data/apportionment/apportionment-2020-table01.xlsx.
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a. The 1960 apportionment was the first to include Hawai and Alaska, which became states in 1959 .
b. Apportionments between 1930 and 1950 occurred with 48 states.
c. No apportionment occurred after the 1920 census.
d. The 1910 apportionment occurred with a House size of 433 and 46 states. Two seats were added to the
House once Arizona and New Mexico became states in 1912.
Figure 2. Changes to Average District Apportionment Population Sizes and House
Seats Over Last Four Apportionment Cycles, 1990-2020

Source: CRS compilation of apportionment population data for 1990 and 2020 from the U.S. Census Bureau.
Graphic created by Amber Hope Wilhelm, CRS Visual Information Specialist.
Federal Requirements/Guidelines for Reapportionment: History
and Current Policy
The constitutional requirements for representation in the House based on state population size are
provided in Article I, Section 2, as amended by Section 2 of the Fourteenth Amendment.7 Article
I, Section 2, specified the first apportionment of seats for the House of Representatives,8 and it
also includes some standards for subsequent reapportionments. Article I, Section 2, requires that
the national population be counted at least once every 10 years in order to distribute House seats
across states. Broad parameters for the number of House Members are also contained in Article I,

7 Article I, Section 2, clause 3, originally stated, “Representatives and direct T axes shall be apportioned among the
several States which may be included within this Union, according to their respective Numbers, which shall be
determined by adding t o the whole Number of free Persons, including those bound to Service for a T erm of Years, and
excluding Indians not taxed, three fifths of all other Persons.” Following the abolition of slavery, the Fourteenth
Amendment, Section 2, states, “ Representatives shall be apportioned among the several States according to their
respective numbers, counting the whole number of persons in each State, excluding Indians not taxed. ” For more
information, see Office of the Historian, U.S. House of Representatives, “ Propo rtional Representation,” at
https://history.house.gov/Institution/Origins-Development/Proportional-Representation/.
8 Article 1, Section 2, provides that a first census would be taken within three years of the first meeting of Congress,
and until the population was formally enumerated by a census, there would be 65 House Members, allocated among
New Hampshire (3), Massachusetts (8), Rhode Island (1), Connecticut (5), New York (6), New Jersey (4),
Pennsylvania (8), Delaware (1), Maryland (6), Virginia (10), North Carolina (5), South Carolina (5), and Georgia (3).
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Section 2: there can be no more than one Representative for every 30,000 persons, provided that
each state receives at least one Representative.
Federal statute establishes a number of other elements of the apportionment process, including
how to count the population every 10 years via the decennial census; how many seats are in the
House; how those House seats are divided across states; and certain related administrative details.
In the 19th century, Congress often passed measures each decade to address those factors
specifical y for the next upcoming census and reapportionment. By the early 20th century,
however, Congress began to create legislation to standardize the process and apply it to al
subsequent censuses and reapportionments, unless modified by later acts.9
One example of such legislation was the permanent authorization of the U.S. Census Bureau in
1902,10 which helped establish a recurring decennial census process and timeline. Other
legislation established the current number of 435 House seats;11 this number was first used
following the 1910 census and subsequently became fixed under the Permanent Apportionment
Act of 1929.12 Congress also created a more general reapportionment formula and process to
redistribute seats across states. The timeline for congressional reapportionment and current
method for al ocating seats among states were contained in the Apportionment Act of 1941,
which would then apply to every reapportionment cycle, beginning with the one following the
1950 census.13 The size of the House, method for reapportionment, and timeline for
reapportionment are codified in 2 U.S.C. §2a and are further detailed in the section below,
alongside the relevant census procedures codified in Title 13 of the U.S. Code.
Reapportionment Method and Timeline
The apportionment steps detailed below are also summarized by the timeline in Figure 1. This
information is representative of the typical census, apportionment, and redistricting processes, but
the Coronavirus Disease 2019 (COVID-19) pandemic affected 2020 census field operations and
delivery of apportionment figures; for further discussion of these changes and delays, see CRS In
Focus IF11486, 2020 Census Fieldwork Delayed by COVID-19 and CRS Insight IN11360,
Apportionment and Redistricting Following the 2020 Census.
Under federal law, April 1 in any year ending in “0” marks the official decennial census date and
the beginning of the population counting process.14 The U.S. Census Bureau calculates the

9 For one overview of provisions contained in various apportionment acts, see Emanuel Celler, “Congressional
Apportionment—Past, Present, and Future,” Law and Contem porary Problem s, vol. 17, no. 2 (Spring 1952), pp. 268 -
275, at https://scholarship.law.duke.edu/lcp/vol17/iss2/3/. Copies of past apportionment acts (1790 -1941) are available
from the U.S. Census Bureau at https://www.census.gov/history/www/reference/apportionment .
10 13 U.S.C. §2 note.
11 T his excludes the nonvoting House seats held by Delegates and the Resident Commissioner; Article I, Section 2, and
resulting apportionment practices, only address Representatives from U.S. states.
12 T he 1910 apportionment act (P.L. 62-5, August 8, 1911, 37 Stat. 13, Ch. 5) set the House size at 433, but provided
for the addition of one seat each to New Mexico and Arizona, if they became states before the next apportionment,
which they did. T he next enacted apportionment bill was the Permanent Apportionment Act of 1929 (P.L. 71-13, June
18, 1929, 26 Stat. 21, Ch. 28), which preserved the methods of the preceding apportionment for subsequent
apportionments. The enabling acts for Alaska and Hawaii statehood provided temporary increases in the size of the
House to provide seats for the new states until the next regular reapportionment, and as a result, the House had 437
seats between 1959 and 1962. See P.L. 85 -508, July 7, 1958; P.L. 86-3, March 18, 1959, 73 Stat. 4.
13 P.L. 77-291, November 15, 1941, 55 Stat. 761, Ch. 470. Similar provisions were contained in the Permanent
Reapportionment Act of 1929.
14 13 U.S.C. §141(a). For additional information on the census process, see CRS Report R44788, The Decennial
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apportionment population for the United States from the information it collects in the decennial
census and certain administrative records.15 The apportionment population reflects the total
resident population in each of the 50 states, including minors and noncitizens, plus Armed Forces
personnel/dependents living overseas and federal civilian employees/dependents living
overseas.16 The Secretary of Commerce must report the apportionment population to the President
within nine months of the census date (by December 31 of the year ending in “0”).17 In past years,
the Census Bureau has released apportionment counts to the public at about the same time they
are presented to the President.18
Under requirements in the Constitution, each state must receive at least one House
Representative, and under statute, the current House size is set at 435 seats.19 To determine how
the 51st through 435th seats are distributed across the 50 states, a mathematical approach known as
the method of equal proportions is used, which is specified in statute.20 Essential y, under this
method, the “next” House seat available is apportioned to the state ranked highest on a priority
list
. The priority list rankings are calculated by taking each state’s apportionment population from
the most recent census, and multiplying it by a series of values. The multipliers used are the
reciprocals of the geometric means between every pair of consecutive whole numbers, with those
whole numbers representing House seats to be apportioned.21 The resulting priority values are
ordered from largest to smal est, and with the House size set at 435, the states with the top 385
priority values receive the available seats. See the Appendix for additional information on the
method of equal proportions and other methods proposed or used in previous apportionments.
The President then transmits a statement to Congress showing (1) “the whole number of persons
in each State,” as determined by the decennial census and certain administrative records; and (2)
the resulting number of Representatives each state would be entitled to under an apportionment,
given the existing number of Representatives and using the method of equal proportions. The
President submits this statement to Congress within the first week of the first regular session of

Census: Issues for 2020; and CRS In Focus IF11015, The 2020 Decennial Census: Overview and Issues.
15 13 U.S.C. §141(b).
16 For further discussion of who is included in apportionment population counts, see U.S. Census Bureau,
“Congressional Apportionment: Frequently Asked Questions,” August 26, 2015, at https://www.census.gov/topics/
public-sector/congressional-apportionment/about/faqs.html.
17 13 U.S.C. §141(b).
18 For example, see U.S. Census Bureau, “U.S. Census Bureau Announces 2010 Census Population Counts
Apportionment Counts Delivered to President,” press release, December 21, 2010, at https://www.census.gov/
newsroom/releases/archives/2010_census/cb10-cn93.html.
19 Permanent Apportionment Act of 1929, P.L. 71-13, June 18, 1929, 26 Stat. 21, Ch. 28.
20 P.L. 77-291, November 15, 1941, 55 Stat. 761, Ch. 470. T he method of equal proportions is sometimes referred to as
the Huntington-Hill m ethod. Prior to the 1941 act, other apportionment methods could be used; one such alternative
used in several reapportionments was the Webster m ethod. Generally, these apportionment methods vary in how they
approach fractional seat entitlements and what rounding points should be used in order to distribute those fractions of
seats across states. For a discussion of alternate mathematical approaches, see U.S. Census Bureau, “ Methods of
Apportionment,” July 18, 2017, at https://www.census.gov/history/www/reference/apportionment/
methods_of_apportionment.html; and Laurence F. Schmeckebier, “ T he Method of Equal Proportions,” Law and
Contem porary Problem s
, vol. 17, no. 2 (Spring 1952), pp. 302 -313.
21 A geometric mean is the square root of the product of two successive numbers multiplied by each other; the
reciprocal of a geometric mean is 1 divided by the geometric mean. T o find the “multiplier” for each state’s second
seat, for example, the geometric mean of 1 and 2 would be used; 1 multiplied by 2 equals 2, and the square root of 2 is
1.41452. T he reciprocal of this geometric mean would be 1 divided by 1.41452, or 0.70711. For discussion on the
method of equal proportions, and tables with multipliers and priority values for previous ap portionments, see U.S.
Census Bureau, “Computing Apportionment,” Congressional Apportionment, February 4, 2013, at
https://www.census.gov/population/apportionment/about /computing.html.
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the next Congress (typical y, early January of a year ending in “1”).22 Within 15 calendar days of
receiving the President’s statement, the Clerk of the House sends each state governor a certificate
indicating the number of Representatives the state is entitled to. Each state receives the number of
Representatives noted in the President’s statement for its House delegation, beginning at the start
of the next session of Congress (typical y, early January of a year ending in “3”).
States may then engage in their own redistricting processes, which vary based on state laws.
Federal law contains requirements for how apportionment changes wil apply to states in the
event that any congressional elections occur between a reapportionment and the completion of a
state’s redistricting process. In these instances, states with the same number of House seats would
use the existing congressional districts to elect Representatives; states with more seats than
districts would elect a Representative for the “new” seat through an at-large election and use
existing districts for the other seats; and states with fewer seats than districts would elect al
Representatives through an at-large election.23
Redistricting Process24
Congressional redistricting involves creating or redrawing geographic boundaries for U.S. House
districts within a state. Redistricting procedures are largely determined by state law and vary
across states, but states must comply with certain parameters established by federal statute and
court decisions. In general, there is variation among states regarding the practice of drawing
districts and which decisionmakers are involved in the process. Across states, there are some
common standards and criteria for districts, some of which reflect values that are commonly
thought of as traditional districting practices. Districting criteria may result either from shared
expectations and precedent regarding what districts should be like, or they may result from
certain standards established by current federal statute and court decisions. These criteria
typical y reflect a goal of enabling “fair” representation for al residents, rather than al owing
arbitrary, or discriminatory, map lines.25
Redistricting efforts intended to unfairly favor one group’s interests over another’s are commonly
referred to as gerrymandering.26 Packing and cracking are two common terms that describe such
districts, but there are various ways in which district boundaries might be designed to advantage
or disadvantage certain groups of voters. Packing describes district boundaries that are drawn to
concentrate individuals who are thought to share similar voting behaviors into certain districts.
Concentrating prospective voters with shared preferences can result in a large number of “wasted

22 P.L. 77-291, November 15, 1941, 55 Stat. 761, Ch. 470. T he statute is written to apply to the first regular session of
the 82nd Congress “ and of each fifth Congress thereafter.”
23 2 U.S.C. §2a(c).
24 T his report is not intended to be a legal analysis. For additional information on redistricting law, see CRS Report
R44199, Congressional Redistricting: Legal and Constitutional Issues; and CRS Report R44798, Congressional
Redistricting Law: Background and Recent Court Rulings
.
25 For further discussion, see Jeanne C. Fromer, “An Exercise in Line-Drawing: Deriving and Measuring Fairness in
Redistricting,” Georgetown Law Journal, vol. 93 (2004-2005), pp. 1547-1623.
26 Michael Wines, “What Is Gerrymandering? What If the Supreme Court Bans It?” New York Times, March 26, 2019,
at https://www.nytimes.com/2019/03/26/us/what -is-gerrymandering.html; John O’Loughlin, “ T he Identification and
Evaluation of Racial Gerrymandering,” Annals of the Association of American Geographers, vol. 72, no. 2 (June 1982),
pp. 165-184; John N. Friedman and Richard T . Holden, “ T he Rising Incumbent Reelection Rate: What’s
Gerrymandering Got to Do With It?” Journal of Politics, vol. 71, no. 2 (April 2009), pp. 593-611; CRS Legal Sidebar
LSB10164, Partisan Gerrym andering: Suprem e Court Provides Guidance on Standing and Maintains Legal Status
Quo
.
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votes” for these districts, as their Representatives wil often be elected by a supermajority that far
exceeds the number of votes required for a candidate to win. Cracking may be thought of as the
opposite of packing, and occurs when individuals who are thought to share similar voting
preferences are deliberately dispersed across a number of districts. This approach dilutes the
voting strength of a group and can prevent its preferred candidates from receiving a majority of
the vote in any district.
For some states, redistricting following an apportionment may be necessary to account for House
seats gained or lost based on the most recent census population count.27 General y, however,
states with multiple congressional districts engage in redistricting following an apportionment in
order to ensure that the population size of each district remains approximately equal under the
equality standard or “one person, one vote” principle (discussed under “Population Equality”
below). Some states might make additional changes to district boundaries in the years following
an initial redistricting; in some instances, such changes are required by legal decisions finding
that the initial districts were improperly drawn.28
Federal Requirements/Guidelines for Redistricting: History and
Current Policy
From time to time, Congress considers legislation that would affect apportionment and
redistricting processes. The Constitution requires the apportionment of House seats across states
based on population size, but it does not specify how those seats are to be distributed within each
state. Most redistricting practices are determined by state constitutions or statutes, although some
parts of the redistricting process are affected by federal statute or judicial interpretations.29
The current system of single-member districts (rather than a general ticket system, where voters
could select a slate of Representatives for an entire state) is provided by 2 U.S.C. §2c.30 In
addition to requiring single-member districts, Congress has, at times, passed legislation
addressing House district characteristics. For example, in the 1800s and early 1900s, some federal
apportionment statutes included other standards for congressional districts, such as population
equality or geographic compactness.31 None of these criteria is expressly contained in the current
statute addressing federal apportionment.32

27 Table 1 provides information on which states gained and lost seats following the 2020 census, and Table 2 provides
additional historical data on the number of states and House seats affected by each apportionment since 1910.
28 CRS Report R44798, Congressional Redistricting Law: Background and Recent Court Rulings.
29 Ibid.
30 P.L. 90-196, December 14, 1967, 81 Stat. 581. The requirement for single-member districts had previously appeared
in the Apportionment Act of 1842 (June 25, 1842, 5 Stat. 491). For additional history, see Erik J. Engstrom, “T he
Origins of Single-Member Districts,” ch. 3 in Partisan Gerrym andering and the Construction of Am erican Dem ocracy
(Ann Arbor, MI: University of Michigan Press, 2013), pp. 43 -55.
31 Examples include a requirement for equal population size “as nearly as practicable” ( “An Act for the Apportionment
of Representatives to Congress among the several States according to the ninth Census,” February 2, 1872, 17 Stat. 28);
and districts of “ contiguous and compact territory” (“An Act Making an apportionment of Representatives in Congress
among the several States under the T welfth Census,” January 16, 1901, 31 Stat. 733; “ An Act for the apportionment of
Representatives in Congress among the several States under the T hirteenth Census, ” P.L. 62-5, August 8, 1911, 37 Stat.
13, Ch. 5). Some of these provisions appeared in several subsequent apportionment bills.
32 P.L. 77-291, November 15, 1941, 55 Stat. 761, Ch. 470.
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Many of the other federal parameters for congressional redistricting have resulted from judicial
decisions.33 It is not uncommon for states to face legal chal enges regarding elements of their
redistricting plans.34 One analysis of the 2010 redistricting cycle, for example, found that
redistricting lawsuits had been filed in 38 states,35 and legal chal enges to congressional districts
in several states continued for a number of years.36 This report is not intended to be a legal
analysis. For additional information on redistricting law, see CRS Report R44199, Congressional
Redistricting: Legal and Constitutional Issues, and CRS Report R44798, Congressional
Redistricting Law: Background and Recent Court Rulings.
Population Equality
One area of redistricting addressed by federal standards is population equality across districts.
Legislative provisions, requiring that congressional districts “[contain] as nearly as practicable an
equal number of inhabitants,” were found in federal apportionment acts between 1872 and 1911.37
The U.S. Supreme Court has also addressed population size variance among congressional
districts within a state, or malapportionment. Under what is known as the “equality standard” or
“one person, one vote” principle, the Court has found congressional districts within a state should
be drawn to approximately equal population sizes.38 Mathematical y, there are several ways in
which the population difference across districts (or deviation from an ideal district size) may be
expressed.39
These equal population standards apply only to districts within a state, not to districts across
states. To il ustrate how district population sizes can vary across states, Table 3 provides Census
Bureau estimates from 1910 to 2020 for the average district population size nationwide, as wel as
estimates for which states had the largest and smal est average district population sizes. Wide
variations in state populations and the U.S. Constitution’s requirement of at least one House seat
per state make it difficult to ensure equal district sizes across states, particularly if the size of the

33 See CRS Report R44798, Congressional Redistricting Law: Background and Recent Court Rulings, for additional
information.
34 Adam Mueller, “T he Implications of Legislative Power: State Constitutions, State Legislatures, and Mid-Decade
Redistricting,” Boston College Law Review, vol. 48 (2007), p. 1344.
35 “Redistricting Lawsuits Relating to the 2010 Census,” Ballotpedia, updated September 2015, at
https://ballotpedia.org/Redistricting_lawsuits_relating_to_the_2010_Census.
36 For one listing of litigation across states for both congressional districts and state legislative districts, see Michael Li,
T homas Wolf, and Annie Lo, “T he State of Redistricting Litigation,” Brennan Center for Justice, April 1, 2021, at
https://www.brennancenter.org/blog/state-redistricting-litigation. See also “ Redistricting Lawsuits Relating to the 2010
Census,” Ballotpedia, updated September 2015, at https://ballotpedia.org/
Redistricting_lawsuits_relating_to_the_2010_Census. T hese resources provide examples of some recent legal
challenges but may not represent a comprehensive account of all cases.
37 Historical apportionment acts can be viewed at U.S. Census Bureau, “Apportionment Legislation 1840-1880,”
History, at https://www.census.gov/history/www/reference/apportionment/apportionment_legislation_1840_-
_1880.html; U.S. Census Bureau, “ Apportionment Legislation 1890 -Present,” History, at https://www.census.gov/
history/www/reference/apportionment/apportionment_legislation_1890_-_present.html.
38 See CRS Report R44798, Congressional Redistricting Law: Background and Recent Court Rulings.
For an overview of these, and related, Supreme Court cases, see National Conference of State Legislatures, “ Cases
Relating to Population,” in Redistricting and the Supreme Court: The Most Significant Cases, July 19, 2018, at
http://www.ncsl.org/research/redistricting/redistricting-and-the-supreme-court -the-most-significant-cases.aspx; also
National Conference of State Legislatures, “ Equal Population,” in Redistricting Law 2010, December 1, 2009, ch. 3, at
http://www.ncsl.org/research/redistricting/redistricting-law-2010.aspx.
39 See National Conference of State Legislatures, “Measuring Population Equality Among Districts,” in Redistricting
Law 2010
, December 1, 2009, pp. 23-25, at http://www.ncsl.org/research/redistricting/redistricting-law-2010.aspx.
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House is fixed.40 The expectation that districts in a state wil have equal population sizes
reinforces the long-standing practice that states redraw district boundaries following each U.S.
Census, in order to account for the sizable population shifts that can occur within a 10-year
span.41
Table 3. Summary of Average U.S. House District Population Sizes, 1910-2020
Apportionment
Average District
Largest Average
Smallest Average
Year
Population Size
District Population
District Population
2020
761,169
990,837 (Delawarea)
542,704 (Montana)
2010
710,767
994,416 (Montanaa)
527,624 (Rhode Island)
2000
646,952
905,316 (Montanaa)
495,304 (Wyominga)
1990
572,466
803,655 (Montanaa)
455,975 (Wyominga)
1980
519,235
690,178 (South Dakotaa)
393,345 (Montana)
1970
469,088
624,181 (North Dakotaa) 304,067 (Alaskaa)
1960b
410,481
484,633 (Maine)
226,167 (Alaskaa)
1950c
344,587
395,948 (Rhode Island)
160,083 (Nevadaa)
1940c
301,164
359,231 (Vermonta)
110,247 (Nevadaa)
1930c
280,675
395,982 (New Mexicoa)
86,390 (Nevadaa)
1920d



1910e
210,328
228,027 (Washington)
80,293 (Nevadaa)
Source: U.S. Census Bureau, Historical Apportionment Data (1910-2020), at https://www.census.gov/data/tables/
time-series/dec/apportionment-data-text.html.
a. State had a single House district during the noted apportionment year.
b. The 1960 apportionment was the first to include Hawai and Alaska, which became states in 1959.
c. Apportionments between 1930 and 1950 occurred with 48 states.
d. No apportionment occurred after the 1920 Census.
e. The 1910 apportionment occurred with a House size of 433 and 46 states. Two seats were added to the
House once Arizona and New Mexico became states in 1912.
To assist states in drawing districts that have equal population sizes, the Census Bureau provides
population tabulations for certain geographic areas identified by state officials, if requested, under
the Census Redistricting Data Program, created by P.L. 94-171 in 1975. Under the program, the
Census Bureau is required to provide total population counts for smal geographic areas; in
practice, the Bureau also typical y provides additional demographic information, such as race,
ethnicity, and voting age population, to states.42

40 U.S. Census Bureau, Historical Apportionment Data (1910-20202), at https://www.census.gov/data/tables/time-
series/dec/apportionment -data-text.html. See also Drew Desilver, “ U.S. Population Keeps Growing, But House of
Representatives Is Same Size As in T aft Era,” FactTank, Pew Research Center, May 31, 2018, at
https://www.pewresearch.org/fact-tank/2018/05/31/u-s-population-keeps-growing-but-house-of-representatives-is-
same-size-as-in-taft-era/.
41 Adam Mueller, “T he Implications of Legislative Power: State Constitutions, State Legislatures, and Mid-Decade
Redistricting,” Boston College Law Review, vol. 48 (2007), p. 1351.
42 P.L. 94-171, December 23, 1975, 89 Stat. 1023; 13 U.S.C. §141(c). See also U.S. Census Bureau, “Redistricting
Data Program Management,” updated December 27, 2018, at https://www.census.gov/programs-surveys/decennial-
census/about/rdo/program-management.html; and Catherine McCully, Designing P.L. 94-171 Redistricting Data for
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Racial/Language Minority Protections43
The Voting Rights Act of 1965 (VRA) also affects how congressional districts are drawn. One key
statutory requirement for congressional districts comes from Section 2 of the VRA, as amended,
which prohibits states or their political subdivisions from imposing any voting qualification,
practice, or procedure that results in denial or abridgement of the right to vote based on race,
color, or membership in a language minority.44 Under the VRA, states cannot draw district maps
that have the effect of reducing, or diluting, minority voting strength.45
Other Redistricting Considerations
In addition to requirements of population equality and compliance with the VRA, several other
redistricting criteria are common across many states today, including compactness, contiguity,
and observing political boundaries.46 Some of the common redistricting criteria specified by states
are presented in Table 4. These factors are sometimes referred to as traditional districting
principles and are often related to geography. The placement of district boundaries, for example,
might reflect natural features of the state’s land; how the population is distributed across a certain
land area; and efforts to preserve existing subdivisions or communities (such as town boundaries
or neighborhood areas). Redistricting laws in many states currently include such criteria, but they
are not explicitly addressed in current federal statute. Previous federal apportionment statutes,
however, sometimes contained similar provisions.
Table 4. Selected Congressional Redistricting Criteria Specified by Certain States
f
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AL
Yes
Yes
Yes
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Yesa
AZ
Yes
Yes
Yes
Yes
Yes


CA
Yes
Yes
Yes
Yes



CO
Yes
Yes
Yes
Yes
Yes


FL
Yes
Yes
Yes




GA
Yes
Yes
Yes
Yes


Yesa

the Year 2020 Census: The View from the States, U.S. Census Bureau, Washington, DC, December 2014, at
https://www.census.gov/library/publications/2014/rdo/pl94-171.html.
43 T his report is not intended to be a legal analysis of these topics; for additional information on related redistricting
law, see CRS Report R44199, Congressional Redistricting: Legal and Constitutional Issues; and CRS Report R44798,
Congressional Redistricting Law: Background and Recent Court Rulings.
44 52 U.S.C. §§10301, 10303(f)(2).
45 52 U.S.C. §10304; for further discussion, see CRS Report R44798, Congressional Redistricting Law: Background
and Recent Court Rulings
, pp. 6-12.
46 An overview of common districting principles, and a chart detailing current requirements across states, are available
in National Conference of State Legislatures, “ Redistricting Criteria,” April 23, 2019, at http://www.ncsl.org/research/
redistricting/redistricting-criteria.aspx. For an overview of how certain criteria have been applied over time, see Micah
Altman, “T raditional Districting Principles: Judicial Myths vs. Reality,” Social Science History, vol. 22, no. 2 (Summer
1998), pp. 159-200.
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f
s o




g
ie
e


in
us
ns
iv
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pact
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ubdiv
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reserve
vo
S
C
C
P
S
C
Interest
C
P
“C
A
Incum
HI
Yes
Yes

Yes



ID
Yes
Yes
Yes
Yes



IA
Yes
Yes
Yes




KS
Yes
Yes
Yes
Yes

Yes

KY

Yes
Yes
Yes



LA

Yes
Yes


Yes

ME
Yes
Yes
Yes




MI
Yes
Yes
Yes
Yes

Yes

MN
Yes
Yes
Yes
Yes



MS
Yes
Yes
Yes
Yes


Yesa
MO
Yes
Yes





MT
Yes
Yes
Yes




NE
Yes
Yes
Yes


Yes

NV
Yes
Yes
Yes


Yes
Yes
NM
Yes
Yes
Yes
Yes

Yesa
Yesa
NY
Yes
Yes
Yes
Yes
Yes
Yes

NC
Yes
Yes
Yes



Yesa
OH
Yes
Yes
Yes
Yes



OK
Yes
Yes
Yes
Yes



OR
Yes
Yes
Yes
Yes



PA
Yes
Yes
Yes




RI
Yes
Yes
Yes




SC
Yes
Yes
Yes
Yes

Yes
Yes
TX

Yes
Yes




UT
Yes
Yes
Yes
Yes



VA
Yes
Yes

Yes



WA
Yes
Yes
Yes
Yes
Yes


WV
Yes
Yes
Yes




WYb
Yes
Yes
Yes




Source: National Conference of State Legislatures, “Redistricting Systems: A 50-State Overview,” March 29,
2021, at https://www.ncsl.org/research/redistrict ing/redist ricting-systems-a-50-state-overview.aspx; and individual
state pages linked from Bal otpedia, “State-by-State Redistricting Procedures,” at https://bal otpedia.org/State-by-
state_redistricting_procedures. Additional information may be available from individual states. See the fol owing
text sections for an explanation of the criteria used as column headings in this table.
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Notes: States excluded from this table do not specify any of these criteria for congressional redistricting. These
states are Alaska, Arkansas, Connecticut, Delaware, Il inois, Indiana, Maryland, Massachusetts, New Hampshire,
New Jersey, North Dakota, South Dakota, Tennessee, Vermont, and Wisconsin. Some of these states (Alaska,
Delaware, North Dakota, South Dakota, and Vermont) currently have a single House seat. Some states specify
different criteria for state legislative districts.
a. Factor is something that state may “al ow” for consideration.
b. State currently only has one congressional district.
Compactness and Contiguity
As a districting criterion, compactness reflects the idea that a congressional district should
represent a geographical y consolidated area.47 Compactness of congressional districts is a
requirement in 32 states, but often, state laws do not specify precise measures of compactness.48
General y, a compact district would tend to have smoother boundaries and might resemble a
standard geometric shape more than a less compact district. In some conceptualizations, a
compact district would have an identifiable “center” that seems reasonably equidistant from any
of its boundaries.49
Federal apportionment acts between 1842 and 1911 contained provisions requiring that
congressional districts be of “contiguous territory,”50 and most states have included similar
language in their current redistricting laws. For a district to be contiguous, it general y must be
possible to travel from any point in the district to any other place in the district without crossing
into a different district.51
Preserving Political Subdivisions
Most states require that redistricting practitioners take into account existing political boundaries,
such as towns, cities, or counties. In many instances, districts may not be able to be drawn in
ways that encompass entire political subdivisions, given other districting standards, like
population equality, that could take precedence. Maintaining political subdivisions can also help
simplify election administration by ensuring that a local election jurisdiction is not split among
multiple congressional districts. Some state laws direct redistricting authorities to preserve the

47 For additional background on compactness as a redistricting principle, see William Bunge, “Gerrymandering,
Geography, and Grouping,” Geographical Review, vol. 56, no. 2 (April 1966), pp. 256-263; Jacob S. Siegel,
“Geographic Compactness vs. Race/Ethnic Compactness and Other Criteria in the Delineation of Legislative Districts,”
Population Research and Policy Review, vol. 15, no. 2 (April 1996), pp. 147 -164; Richard G. Niemi et al., “ Measuring
Compactness and the Role of a Compactness Standard in a T est for Partisan and Racial Gerrymandering,” Journal of
Politics
, vol. 52, no. 4 (November 1990), pp. 1155 -1181; and Daniel D. Polsby and Robert D. Popper, “ The T hird
Criterion: Compactness as a Procedural Safeguard Against Partisan Gerrymandering,” Yale Law and Policy Review,
vol. 9, no. 2 (Spring/Summer 1991), pp. 301 -353.
48 National Conference of State Legislatures, “Redistricting Criteria,” April 23, 2019, at http://www.ncsl.org/research/
redistricting/redistricting-criteria.aspx; for further discussion, see Aaron Kaufman, Gary King, and Mayya
Komisarchik, “How to Measure Legislative District Compactness If You On ly Know It When You See It,” working
paper, updated February 24, 2019, at https://gking.harvard.edu/files/gking/files/compact.pdf, pp. 1-5.
49 See “Compactness” section from Justin Levitt, “Where Are the Lines Drawn?” All About Redistricting, Loyola Law
School, 2020, at http://redistricting.lls.edu/where-state.php#contiguity.
50 Historical apportionment acts can be viewed at U.S. Census Bureau, “Apportionment Legislation 1840 -1880,”
History, at https://www.census.gov/history/www/reference/apportionment/apportionment_legislation_1840_-
_1880.html; U.S. Census Bureau, “ Apportionment Legislation 1890 -Present,” History, at https://www.census.gov/
history/www/reference/apportionment/apportionment_legislation_1890_-_present.html.
51 See “Contiguity” section from Justin Levitt, “Where Are the Lines Drawn?” All About Redistricting, Loyola Law
School, 2020, at https://redistricting.lls.edu/redistricting-101/where-are-the-lines-drawn/#contiguity.
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“core” of existing congressional districts; other states prohibit drawing district boundaries that
would create electoral contests between incumbent House Members.52
Preserving Communities of Interest
Some states include the preservation of communities of interest as a criterion in their redistricting
laws. People within a community of interest general y have a shared background or common
interests that may be relevant to their legislative representation. These rec ognized similarities
may be due to shared social, cultural, historical, racial, ethnic, partisan, or economic factors. In
some instances, communities of interest may natural y be preserved by following other
redistricting criteria, such as compactness or preserving political subdivisions.53
Promoting Political Competition; Considering Existing District or Incumbent
Some states include measures providing that districts cannot be drawn to unduly favor a particular
candidate or political party. The term gerrymander originated to describe districts drawn to favor
a particular political party,54 and it is often used in this context today. Redistricting has
traditional y been viewed as an inherently political process, where authorities have used partisan
considerations in drawing district boundaries. Districts general y may be drawn in a way that is
political y advantageous to certain candidates or political parties, unless prohibited by state law.55
Some states, for example, expressly al ow the use of party identification information in the
redistricting process, whereas others prohibit it; similarly, some states may al ow for practices to
protect an incumbent or maintain the “core” of an existing district, whereas other states prohibit
any practices that would favor or disfavor an incumbent or candidate.56
State Processes for Redistricting
Redistricting processes are fundamental y the responsibility of state governments under current
law and practice. Among the 44 states with multiple House districts, a variety of approaches are
taken, but general y, states either al ow their state legislatures or a separate redistricting
commission to determine congressional district boundaries. The map in Figure 3 displays the
redistricting methods currently used across states.

52 National Conference of State Legislatures, “Redistricting Criteria,” April 23, 2019, at http://www.ncsl.org/research/
redistricting/redistricting-criteria.aspx.
53 See “Communities of interest” section from Justin Levitt, “Where Are the Lines Drawn?” All About Redistricting,
Loyola Law School, 2020, at https://redistricting.lls.edu/redistricting-101/where-are-the-lines-drawn/
#communities+of+interest .
54 In 1812, the term was coined to describe a salamander-shaped state legislative district in Massachusetts that
benefitted Governor Elbridge Gerry’s party. See Erick T rickey, “Where Did the T erm ‘Gerrymander’ Com e From?”
Sm ithsonian Magazine, July 20, 2017, at https://www.smithsonianmag.com/history/where-did-term-gerrymander-
come-180964118/.
55 Cases addressing partisan gerrymandering have recently been heard by the Supreme Court; for more information, see
CRS Legal Sidebar LSB10324, Partisan Gerrym andering Claim s Not Subject to Federal Court Review:
Considerations Going Forward
; CRS Legal Sidebar LSB10276, Suprem e Court Once Again Considers Partisan
Gerrym andering: Im plications and Legislative Options
; and CRS Legal Sidebar LSB10164, Partisan Gerrym andering:
Suprem e Court Provides Guidance on Standing and Maintains Legal Status Quo
.
56 National Conference of State Legislatures, “Redistricting Criteria,” April 23, 2019, at http://www.ncsl.org/research/
redistricting/redistricting-criteria.aspx.
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Figure 3. State Redistricting Methods

Source: CRS compilation, based on information from Bal otpedia and the National Conference of State
Legislatures. Graphic created by Amber Hope Wilhelm, CRS Visual Information Specialist.
Notes: Iowa has nonpartisan legislative staff create its redistricting maps but requires legislative approval to
enact them. In New York, redistricting plans also require gubernatorial approval.
Historical y, and in the majority of states today, congressional district boundaries are primarily
determined by state legislatures. Currently, 36 states authorize their state legislatures to establish
congressional district boundaries. Most of these states enable the governor to veto a redistricting
plan created by the legislature; Connecticut and North Carolina do not al ow a gubernatorial
veto.57
In recent years, other states have begun to use redistricting commissions, which may be more
removed from state legislative politics.58 In 10 states that currently have multiple congressional
districts (Arizona, California, Colorado, Hawai , Idaho, Michigan, Montana, New Jersey,
Virginia, and Washington), redistricting commissions are primarily responsible for redrawing
congressional districts. In four other states (Maine, New York, Rhode Island, and Utah), a
commission serves in an advisory capacity during the redistricting process. Commissions may
also be used as a “backup” or alternate means of redistricting if the legislature’s plan is not
enacted, such as in Connecticut, Indiana, and Ohio.
The composition of congressional redistricting commissions can also vary; many include
members of the public selected by a method intended to be nonpartisan or bipartisan, whereas
other commissions may include political appointees or elected officials, such as in Hawai and
New Jersey. A commission’s membership, the authority granted to it, its relationship to other state
government entities, and other features may affect whether a commission is perceived to be
undertaking an objective process or a more politicized one. Some proponents of redistricting
commissions believe that using independent redistricting commissions can prevent opportunities

57 See “State-by-State Redistricting Procedures,” Ballotpedia, at https://ballotpedia.org//State-by-
state_redistricting_procedures.
58 Wendy Underhill, “Redistricting Commissions: Congressional Plans,” National Conference of State Legislatures,
April 18, 2019, at http://www.ncsl.org/research/redistricting/redistricting-commissions-congressional-plans.aspx.
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for partisan gerrymandering and may create more competitive and representative districts.59
Others, however, believe that political considerations can remain in commission decisionmaking
processes, and that the effect of redistricting methods on electoral competitiveness is overstated.60
For more information on redistricting commissions, see CRS Insight IN11053, Redistricting
Commissions for Congressional Districts.
The timeline for redistricting also varies across states, and can be affected by state or federal
requirements regarding the redistricting process; the efficiency of the legislature, commission, or
other entities involved in drawing a state’s districts; and, potential y, by legal or political
chal enges made to a drafted or enacted redistricting plan.61 In general, the redistricting process
would usual y begin early in a year ending in “1,” once each state has learned how many seats it
is entitled to under the apportionment following the decennial census.62 Many states complete the
process within the next year. After the 2010 reapportionment, for example, Iowa was the first
state to complete its initial congressional redistricting plan on March 31, 2011, and 31 other states
completed their initial plans by the end of 2011. The remaining 11 states with multiple
congressional districts completed their initial redistricting plans by the middle of 2012, with
Kansas becoming the final state to complete its initial plan on June 7, 2012.63 Some states may
redistrict multiple times between apportionments, if al owed under state law or required by a legal
chal enge to the preliminary redistricting.64

59 Katie Zezima and Emily Wax-T hibodeaux, “Voters Are Stripping Partisan Redistricting Power from Politicians in
Anti-Gerrymandering Efforts,” Washington Post, November 7, 2018, at https://www.washingtonpost.com/national/
voters-are-stripping-partisan-redistricting-power-from-politicians-in-anti-gerrymandering-efforts/2018/11/07/
2a239a5e-e1d9-11e8-b759-3d88a5ce9e19_story.html; Lyle Denniston, “ Opinion Analysis: A Cure for Partisan
Gerrymandering?” SCOTUSblog, June 29, 2015, at https://www.scotusblog.com/2015/06/opinion-analysis-a-cure-for-
partisan-gerrymandering/.
60 For example, see Alan Abramowitz, Brad Alexander, and Matthew Gunning, “Don't Blame Redistricting for
Uncompetitive Elections,” PS: Political Science and Politics, vol. 2839, no. 1 (January 2006), pp. 87-90.
61 For general historical background and an analysis of state redistricting timeline considerations, see Erik J. Engstrom,
“T he Strategic T iming of Congressional Redistricting,” ch. 4 in Partisan Gerrymandering and the Construction of
Am erican Dem ocracy
(Ann Arbor, MI: University of Michigan Press, 2013), pp. 59 -79. A number of lawsuits related to
redistricting following the 2010 census remain pending in 2019; see David A. Lieb, “Gerrymandering Lawsuits Are
Pending in a Dozen St ates,” Associated Press, March 21, 2019, at https://apnews.com//
0e7691a32c954975850de9e78b9b73cc. According to one count, lawsuits were filed in 38 states during the 2010
redistricting cycle; see “ Redistricting Lawsuits Related to the 2010 Census,” Ballotpedia, updated April 17, 2019, at
https://ballotpedia.org//Redistricting_lawsuits_relating_t o_the_2010_Census.
62 T he Census Bureau announced that states will be receiving redistricting data based on the 2020 census by September
30, 2021. See James Whitehorne, “Timeline for Releasing Redistricting Data,” U.S. Census Bureau, February 12, 2021,
at https://www.census.gov/newsroom/blogs/random-samplings/2021/02/timeline-redistricting-data.html.
63 Catherine McCully, “T able 3. Redistricting T imelines—Data Delivery and Initial Plan Passage” in Designing P.L.
94-171 Redistricting Data for the Year 2020 Census: The View from the States
, U.S. Census Bureau, Washington, DC,
December 2014, p. 26, at https://www.census.gov/library/publications/2014/rdo/pl94-171.html. For an illustration of
the timeline of how redistricting processes unfolded across states following the 2010 apportionment, see the chart
created by Justin Levitt, “Maps across the 2010 cycle,” All About Redistricting, Loyola Law School, 2020, at
https://redistricting.lls.edu/resources/maps-across-the-cycle-2010-congress/. District maps may also face later legal
challenges that require further adjustments; see Michael Li, T homas Wolf, and Annie Lo, “ T he State of Redistricting
Litigation,” Brennan Center for Justice, April 1, 2021, at https://www.brennancenter.org/blog/state-redistricting-
litigation for a list of ongoing litigation for congressional and state legislative districts.
64 Justin Levitt and Michael P. McDonald, “T aking the ‘Re’ out of Redistricting: State Constitutional Provisions on
Redistricting T iming,” Georgetown Law Journal, vol. 95 (2007), pp. 1247-1285; Adam Mueller, “T he Implications of
Legislative Power: State Constitutions, State Legislatures, and Mid-Decade Redistricting,” Boston College Law
Review
, vol. 48 (2007), pp. 1343-1386.
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Congressional Options Regarding Redistricting
Although redistricting processes in practice today are largely governed by state law, Congress
has, at times, considered an expanded federal government role, which could serve to standardize
certain elements of the redistricting process across states. Given the historical y limited role the
federal government has played in the redistricting process, concerns about federalism may arise in
the context of certain congressional efforts addressing redistricting. The types of legislative
proposals briefly introduced in this section reflect some common examples of redistricting bil s
introduced in recent Congresses; they are not meant to be an exhaustive list of al the options
Congress has considered or could consider related to redistricting.
Some legislative proposals in recent Congresses would establish criteria for districts, such as
population equality, compactness, contiguity, or preservation of existing political subdivisions.65
Bil s have also been introduced that would require states to use independent redistricting
commissions and/or maintain certain standards of public input and transparency regarding the
redistricting process.66 Some congressional bil s include provisions to prevent states from
redistricting more than once following an apportionment, which is a practice sometimes referred
to as “mid-decade redistricting.”67 Other bil s would expand oversight by the Department of
Justice under certain circumstances related to existing requirements of, or proposed amendments
to, the VRA.68
Most of these bil s have been referred to committee but not passed by either chamber. In the 117th
Congress, the House passed H.R. 1, and a similar version of H.R. 1 was also passed by the House
in the 116th Congress. H.R. 1 is a multifaceted bil that addresses multiple areas of election
administration, among other topics; with respect to redistricting, it would require states to use
independent redistricting commissions, adopt certain redistricting criteria, and prohibit mid-
decade redistricting.69
Concluding Observations
Apportionment and redistricting address fundamental elements of representational democracy.
Determining how many elected representatives should serve in the House, and how many people
should be in each congressional district, are central questions for those who are concerned with
how responsive the House can be to the interests of the American public. During earlier eras in

65 Such bills from the 117th Congress to date include H.R. 1, S. 1, and H.R. 80. Such bills from the 116th Congress
included H.R. 1, H.R. 124, H.R. 130, H.R. 1612, H.R. 3572, H.R. 4000, S. 949, S. 1972, and S. 2226. Such bills from
the 115th Congress included H.R. 711, H.R. 712, H.R. 1102, H.R. 3537, H.R. 3848, S. 1880, and S. 3123.
66 Bills from the 117th Congress to date that would require states to use redistricting commissions include H.R. 1, S. 1,
H.R. 80, and H.R. 100. Bills from the 116th Congress that would have required states to use redistricting commissions
included H.R. 1, H.R. 124, H.R. 130, H.R. 163, H.R. 160, H.R. 1612, H.R. 3572, H.R. 4000, S. 949, and S. 2226; bills
from the 115th Congress that would have required states to use redistricting commissions included H.R. 145, H.R. 711,
H.R. 712, H.R. 1102, H.R. 2981, H.R. 3537, H.R. 3848, and S. 1880. Some bills related to redistricting commissions
have also included measures to provide for public input and transparency regarding the redistricting process. Other bills
have included provisions to include public participation in redistricting processes, but would not require states to use
redistricting commissions. T hese bills include H.R. 81 and H.R. 1366 in the 117th Congress to date; similar measures
from previous Congresses included H.R. 131 and H.R. 1799 in the 116th Congress, and H.R. 713 in the 115th Congress.
67 Such bills from the 117th Congress to date include H.R. 1, S. 1, and H.R. 134. Such bills from the 116th Congress
included H.R. 1, H.R. 44, H.R. 124, H.R. 130, H.R. 1612, H.R. 3572, H.R. 4000, S. 949, S. 1972, and S. 2226; such
bills from the 115th Congress included H.R. 711, H.R. 712, H.R. 1102, H.R. 3537, H.R. 3848, and S. 1880.
68 Examples of such bills include H.R. 4 and S. 561 from the 116th Congress and H.R. 151, H.R. 3239, and S. 1419
from the 115th Congress.
69 For additional information and resources, see CRS In Focus IF11097, H.R. 1: Overview and Related CRS Products.
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the United States, the number of seats in the House of Representatives general y increased as the
American population increased, and district sizes could be kept more equal over time and across
states. The House size, however, has been set at 435 seats throughout the last century, while the
national population has continued to grow and concentrate in certain geographic areas, leading to
larger constituencies across al House districts over time and disparate district sizes across states.
Certain elements of the apportionment process are established by the U.S. Constitution. This
includes the requirement for representation in the House based on state population size; the
real ocation of House seats every 10 years upon the completion of a national population count;
and the requirements that each state receives at least one Representative and that there can be no
more than one Representative for every 30,000 persons. Other elements of the process are
addressed through federal legislation, such as the overal number of House seats or method of
distributing seats among the states. Congress more regularly legislated in this area prior to the
mid-20th century, passing decennial acts to address upcoming censuses and apportionments, rather
than creating bil s intended to apply for al future reapportionment cycles.
Whereas apportionment is a process largely governed by federal statute, redistricting is a process,
in practice, largely governed by state law. Certain federal standards apply to House districts,
general y in the interest of preserving equal access to representation, but the method and timeline
by which those districts are created is largely determined by state law. In states with multiple
congressional districts, there are a multitude of ways in which district boundaries can be drawn,
depending upon the criteria used to create the districts. There is often an expectation that
congressional districts wil be drawn in a way that ensures “fair” representation, but “fairness”
can be a somewhat subjective determination.
Many lawmakers and members of the public may agree on some of the more basic
representational principles embedded in apportionment and redistricting law, but can find it
difficult to apply those principles in practice. The criteria commonly used for redistricting today
reflect a combination of state and federal statutes, judicial interpretations, and practices from past
redistricting cycles that may require trade-offs between one consideration and another. Ensuring
equal population size across al congressional districts, for example, may be an agreeable goal for
many individuals. In practice, however, the geographic and demographic distribution of residents
within and across states, coupled with requirements to observe state boundaries, provide al states
with at least one Representative, and maintain a constant number of House seats, make this goal
more difficult to achieve. Although mapmaking software today can design districts with
increasing precision with respect to geographic boundaries and population characteristics, this
technological capacity has not necessarily simplified the overal task of redistricting. A majority
of states faced legal chal enges to congressional district maps drawn following the 2010 census,
reflecting differing perspectives on fairness, representational access, and how competing
redistricting criteria should be weighted.
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Appendix. Determining an Apportionment Method
Congress is a bicameral legislature, in which each state receives equal representation in the
Senate and each state’s representation in the House is based upon its population. Essential y, any
method of apportionment for the House must consider three key variables: (1) the number of
House seats; (2) the number of U.S. states; and (3) the apportionment population of each state. A
mathematical decision must also be made regarding how fractions of seats are addressed, since
House seats must be al ocated as whole numbers, and simple division methods are unlikely to
produce this outcome for al (or any) states. Because the Constitution does not specify a particular
method for apportionment, several options have been considered and utilized throughout history.
When determining apportionment, parameters could be set for the number of seats in the House,
the population size of a district, or both.70 The Constitution, to an extent, addresses House size
and district size by requiring that each state receives at least one House seat and requiring that
there can be no more than one Representative per every 30,000 persons.71 Yet these provisions
provide little practical guidance for what the size of the House or the size of a district should be.
Based on the number of states and U.S. apportionment population from the 2010 Census, for
example, the House could range from a minimum of 50 seats to a maximum size of over 10,000
seats. As a general principle, House size and district size are inversely related: a larger number of
House seats means smal er population sizes for districts, and a smal er number of House seats
means larger population sizes for districts. Attempts by the Framers and various Congresses to
address apportionment reveal a number of perspectives on how best to create a representative
legislature, along with political and logistical considerations related to changes in the size of the
House.72
Prioritizing Equal-Sized Districts or Preserving a Fixed House Size
An apportionment method prioritizing relatively equal district population size would establish a
representation ratio, where there would be one Representative per x number of persons. If the
ratio remains the same across apportionment cycles, increases or decreases in the U.S.
apportionment population would result in corresponding increases or decreases to the total
number of House seats. The representation ratio could also be adjusted to create larger or smal er
districts, in order to limit the magnitude of changes to the overal size of the House. If states
receive fractional al ocations of House seats and there is no constraint on the size of the House, a
simple rounding rule could be utilized to arrive at a whole number of seats for the House overal .
A general example of an apportionment approach prioritizing relatively equal district size
follows:
1. determine an ideal district population size, d;

70 For additional information, see Michael L. Balinski and H. Peyton Young, Fair Representation: Meeting the Ideal of
One Man, One Vote
(New Haven, CT : Yale University Press, 1982); and Efton Park, “ The Mathematics of
Apportionment,” University of Chicago Law School Roundtable, vol. 7, no. 1 (2000), pp. 227-237, available at
https://chicagounbound.uchicago.edu/roundtable/vol7/iss1/9/?.
71 In practice, each House district must also be geographically contained within a state’s boundaries; states can not share
districts.
72 For example, the first amendment proposed by James Madison for the Bill of Rights addressed apportionment, but it
was not ratified. See Akhil Reed Amar, The Bill of Rights (New Haven, CT : Yale University Press, 1998), pp. 8 -17;
and Rosemarie Zagarri, The Politics of Size: Representation in the United States, 1776 -1850 (Ithaca, NY: Cornell
University Press, 1987).
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2. divide each state’s apportionment population, ps1, ps2 … ps50, by d to determine
how many House seats a state would be entitled to (its “quota” of seats), q; and
3. determine a rounding rule to apply for states in which q is not a whole number.73
Until the early 20th century, the size of the House general y increased with each apportionment,
due to the addition of new states and population growth,74 but today, the number of House seats is
set at 435 by federal statute.75 Arguments to expand the House have included expanding the range
of interests that House Members would represent and ensuring that Members remained
knowledgeable about local issues. Yet concerns have also been raised that it would not be feasible
to increase the House size apace with national population growth.76
To be sure that a particular apportionment conforms to a specified size of the House, each state
must receive a whole number of seats, and the sum of al states’ seats must equal the desired total
House size. Many apportionment approaches vary on how to address fractional seats, as
remainders wil often result when calculating state seat quotas. A general example of an
apportionment approach to reach a certain House size follows:
1. a set number of House seats, H, is agreed upon;
2. divide the national apportionment population, pUSA, by H to determine an “ideal”
or average district population size, d, also known as the “initial divisor”;
3. divide each state’s apportionment population, ps1, ps2 … ps50, by d to determine
how many House seats a state would be entitled to (its “quota” of seats), q;
4. determine a rounding rule to apply to any q values that are not whole numbers (to
represent actual House seats, which cannot be divided);77 and
5. add these rounded (or adjusted), q values; if this sum does not equal H, determine
a method to adjust state quotas so that the sum of the resulting q values equals H.
The following discussions provide an introduction to several methods that have been used for
congressional apportionment in the United States. To il ustrate how these methods work, for each
method an imaginary example is provided in the accompanying table, in which the size of the
House is fixed at 20 Members and the seats are divided among four states (states A, B, C, and D)
with the populations specified in the tables.
Hamilton/Vinton Method (Ranking Fractional Remainders)
Congress considered various methods of apportionment after the first census of 1790 and passed
an initial apportionment bil in 1792 that would have utilized what is now known as the
Hamilton/Vinton method. President George Washington, however, exercised his first veto on the
measure, in part, because the resulting apportionment calculations would have violated the

73 An additional decision rule may also be necessary to ensure that each state receives at least one House seat, as
required by the Constitution.
74 An exception occurred in 1842, when the number of House seats decreased; for additional details, see Martin H.
Quitt, “Congressional (Partisan) Constitutionalism: T he Apportionment Act Debate of 1842 and 1844,” Journal of the
Early Republic
, vol. 28, no. 4 (Winter 2008), pp. 627 -651.
75 P.L. 62-5, August 8, 1911, 37 Stat. 13, Ch. 5.
76 For some of these considerations, see summary provided in Christopher St. John Yates, “A House of Our Own or a
House We’ve Outgrown,” Columbia Journal of Law and Social Problems, vol. 25 (1992), pp. 174-187.
77 An additional decision rule may also be necessary to ensure that each state receives at least one House seat, as
required by the Constitution.
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requirement of at least 30,000 persons per district for multiple states.78 Representative Samuel
Vinton later introduced legislation proposing this method, which was enacted, and this
apportionment method was first used in 1850 and continued to inform apportionment
considerations throughout the rest of the 19th century, in conjunction with the Webster method
(discussed below). The Hamilton/Vinton method is based on a fixed House size, H. Each state
receives the whole number of seats in its quota, q, of seats. The remainders from q are rank-
ordered from largest to smal est, and any additional House seats are apportioned to the states with
the largest remainders.
Table A-1. Hamilton/Vinton Method—Sample Apportionment
House size (H) = 20 [Fixed]
Step 1: Find whole number
of seats using d (round
Step 2: Apportion additional seats in order of


down any q remainder)
largest fractional remainders
Additional
Total
State
Population
Quota (q)a
Seats
Remainder
Rank
Seat(s)
Seats
A
2,560
2,560 / 594.1 = 4.31
4
.31
4th
0
4
B
3,315
3,315 / 594.1 = 5.58
5
.58
2nd
1
6
C
995
995 / 594.1 = 1.67
1
.67
1st
1
2
D
5,012
5,012 / 594.1 = 8.44
8
.44
3rd
0
8
Total
11,882

18


2
20
Source: Adapted from U.S. Census Bureau, “Methods of Apportionment,” at https://www.census.gov/history/
www/reference/apportionment/methods_of_apportionment.html.
a. The denominator here is calculated by dividing the national apportionment population ( pUSA = 11,882) by the
number of House seats (H = 20).
Jefferson Method (Largest Divisors)
Following the presidential veto of the Hamilton method, Congress adopted the Jefferson method
of apportionment, which was used from 1792 to 1832. The Jefferson method for apportionment is
based on a fixed House size, H, and each state’s quota of seats, q, is rounded down to the nearest
whole number. Often, the sum of the rounded-down q values is less than H. When this occurs,
divisor values smal er than d are tested until an adjusted divisor, dadj, is found that results in a set
of q values which, when rounded down, sum to H.

78 Although the method contained in the bill was a product of congressional debate, it has become associated with
Secretary of State Alexander Hamilton. President Washington sought opinions from his Cabinet on the apportionment
bill, and Hamilton wrote in support of this approach; Hamilton’s letter is available at https://founders.archives.gov/
documents/Hamilton/01-11-02-0189-0002. See also Balinski and Young, ch. 3.
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Table A-2. Jefferson Method—Sample Apportionment
House size (H) = 20 [Fixed]
Step 1: Find seats if apportioned
using initial divisor, d (round
Step 2: Apportion seats using


down any q remainder)
adjusted divisor, dadja
State
Population
Quota (q)b
Seats
Quota
Total Seats
A
2,560
2,560 / 594.1 = 4.31
4
2,560 / 550 = 4.65
4
B
3,315
3,315 / 594.1 = 5.58
5
3,315 / 550 = 6.03
6
C
995
995 / 594.1 = 1.67
1
995 / 550 = 1.81
1
D
5,012
5,012 / 594.1 = 8.44
8
5,012 / 550 = 9.11
9
Total
11,882

18

20
Source: Adapted from U.S. Census Bureau, “Methods of Apportionment,” at https://www.census.gov/history/
www/reference/apportionment/methods_of_apportionment.html.
a. The regular divisor, d, is often used as a starting point to inform what values could work for an adjusted
divisor, dadj. Here, 550 is used as the adjusted divisor value, but any integer between 513 or 552 would also
produce a series of q values that, when rounded down, sum to the total House size of 20 seats.
b. The denominator here is calculated by dividing the national apportionment population (pUSA = 11,882) by the
number of House seats (H = 20).
Webster Method (Major Fractions)
Some believed that the Jefferson method favored large states, and the Webster method was an
approach first used for apportionment in 1842 and last used for apportionment following the 1930
census. The Webster method is similar to the Hamilton/Vinton method but differs in how it
addresses remainders of seats. Each state receives the whole number of seats in its quota, q; then,
q remainders greater than or equal to 0.5 are rounded up to the next whole number, and those
states receive an additional seat. The example provided in Table A-3 happens to result in the
same number of House seats as the other examples in this appendix, which treat the House size,
H, as fixed at 20 seats, but performing these initial calculations under the Webster method could
result in a subsequent adjustment to the number of House seats.79 If the House size remains fixed,
and the initial sum of seats produced by the Webster method does not equal the desired number of
seats, an adjusted divisor, dadj, can be used to calculate q values that, when rounded and summed,
result in a specific House size.

79 For example, the rounding rule could result in a larger number of House seats (i.e., if each state’s q had a remainder
of 0.5 or above) or smaller number of House seats (i.e., if each state’s q had a remainder lower than 0.5) than expected.
Exceptions to the Webster method “rule” would have to be made for any state receiving a quota of less than 0.5 so that
the state would receive one House seat, as required by the Constitution.
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Table A-3. Webster Method—Sample Apportionment
Step 1: Find whole number of
seats using d (round down any
Step 2: Apportion additional seat to state if


q remainder)
quota remainder ≥ 0.5
State
Population
Quota (q)a
Seats
Remainder
Additional Seat
Total Seats
A
2,560
2,560 / 594.1 = 4.31
4
.31
0
4
B
3,315
3,315 / 594.1 = 5.58
5
.58
1
6
C
995
995 / 594.1 = 1.67
1
.67
1
2
D
5,012
5,012 / 594.1 = 8.44
8
.44
0
8
Total
11,882

18

2
20
Source: Adapted from U.S. Census Bureau, “Methods of Apportionment,” at https://www.census.gov/history/
www/reference/apportionment/methods_of_apportionment.html.
a. The denominator here is calculated by dividing the national apportionment population (pUSA = 11,882) by
the number of House seats (H = 20).
Huntington-Hill Method (Method of Equal Proportions)
In addition to treating large and smal states similarly, some have also believed that an
apportionment method should minimize percentage differences in district population sizes (across
states) as much as possible. The method of equal proportions, also known as the Huntington-Hil
method, seeks to achieve this objective, and has been used for al House apportionments since
1941. This method differs from the Webster method by rounding up remainders for a state’s
quota, q, at the geometric mean, G, rather than at the arithmetic mean. The geometric mean is
found by multiplying two successive numbers together, then taking the square root of their
product; here, the successive numbers represent a state’s q rounded down to the nearest whole
number (its “lower” quota) and a state’s q rounded up to the nearest whole number (its “upper”
quota). Each state receives its “lower” quota of seats and then may receive an additional seat if its
quota, q, is greater than or equal to its geometric mean, G.
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Table A-4. Huntington-Hil Method—Sample Apportionment
House size (H) = 20 [Fixed]
Step 1: Find lower quota (round
down any q remainder) and upper
Step 2: Apportion additional seat to


quota (round up any q remainder)
state if quota ≥ geometric mean
Lower
Upper
Geometric
Additional Seat
Total
State
Population
Quota (q)a
Quota
Quota
Mean (G)
(If q G)
Seats
A
2,560
2,560 / 594.1 = 4.31 4
5
√(4x5) = 4.47
0
4
B
3,315
3,315 / 594.1 = 5.58 5
6
√(5x6) = 5.48
1
6
C
995
995 / 594.1 = 1.67
1
2
√(1x2) = 1.41
1
2
D
5,012
5,012 / 594.1 = 8.44 8
9
√(8x9) = 8.49
0
8
Total
11,882

18
22


2
20
Source: Adapted from U.S. Census Bureau, “Methods of Apportionment,” at https://www.census.gov/history/
www/reference/apportionment/methods_of_apportionment.html.
a. The denominator here is calculated by dividing the national apportionment population (pUSA = 11,882) by
the number of House seats (H = 20).
The initial calculation for a state’s quota, q, under the method of equal proportions, is made by
using the “ideal” district size, d, as the divisor. Table A-4 provides a sample apportionment in
which the sum of the rounded geometric means happens to result in the desired House size, H, of
20 seats, but, in practice, this often does not occur. If the sum of the rounded geometric means for
each state does not result in the desired number of House seats, there is an additional step: seats
can be apportioned using a priority list, which essential y ranks each state’s claim to the “next”
House seat apportioned (i.e., the 51st-435th seats), after each state receives the one seat it is
constitutional y entitled to.
To generate a priority list, each state’s apportionment population is multiplied by a series of
multiplier values. The multiplier values are created using the reciprocal of the geometric mean
associated with each potential successive seat number for the state (above its constitutional y
mandated first seat). For example, the multiplier value for a second House seat in any state would
be 1/√(1 x 2) or 0.707, the multiplier for a third House seat would be √(2 x 3) or 0.408, and so
on.80 The products that result from multiplying these values by each state’s apportionment
population are ranked from largest to smal est to create the priority list, and seats are distributed
until H number of seats (currently 385, the number needed to get to a total of 435 seats once each
of the 50 states receives its constitutional y required seat) have been apportioned.

80 T he Census Bureau typically calculates and provides a list of priority values for each apportionment; for the 2010
priority list, see U.S. Census Bureau, “ 2010 Census Apportionment Results,” December 2010, at
https://www.census.gov/data/tables/2010/dec/2010-apportionment-data.html.
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link to page 29 link to page 29 Apportionment and Redistricting Process for the U.S. House of Representatives

Table A-5. Sample Priority Values and Resulting Priority List for Selected Values
House size (H) = 20 [Fixed]

2nd
3rd
4th
5th
6th
7th
8th
9th

State
Population
Seat
Seat
Seat
Seat
Seat
Seat
Seat
Seat

Priority Valuesa

A
2,560
1,810
1,045
739
572
467
395
342
302

B
3,315
2,344
1,353
957
741
605
512
443
391

C
995
704
406
287
222
182
154
133
117

D
5,012
3,544
2,046
1,447
1,121 915
773
670
591













Total
Corresponding Priority List Rankingb
Seats
A
2,560
4
8
13
18
22
27
32
36
4
B
3,315
2
6
9
12
16
20
23
28
6
C
995
14
25
38
51
62
75
86
98
2
D
5,012
1
3
5
7
10
11
15
17
8
Total
11,882








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Source: CRS calculation.
a. Each priority value is calculated by multiplying the state’s apportionment population by a multiplier,
representing the reciprocal geometric mean of the last seat apportioned and the next seat to be apportioned.
For seat number, n, the multiplier is 1 / (√((n-1) x n). For a list of multipliers, see U.S. Census Bureau,
“Apportionment: Table of Multipliers using the Method of Equal Proportions,” October 17, 2000, at
https://www.census.gov/population/apportionment/files/atable.txt. In this table, priority values are rounded to
the nearest whole number.
b. Values italicized and in bold represent the 16 remaining seats to be apportioned, after each state receives
one seat as constitutional y required and assuming a House size of 20. Larger values in this table are not
consecutive because this table only includes rankings associated with the first nine additional seats to be
apportioned. Larger states could be ranked higher and entitled to additional seats (above nine) before smal er
states receive any additional seats. In this example, if the priority list table continued to display values for
additional seats, State D would be ranked 19th and would receive its 10th seat before State B receives its 7th
seat (ranked 20th); State D is also ranked 21st and would receive its 11th seat before State A receives its 6th
seat (ranked 22nd).


Author Information

Sarah J. Eckman

Analyst in American National Government

Congressional Research Service

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Apportionment and Redistricting Process for the U.S. House of Representatives



Disclaimer
This document was prepared by the Congressional Research Service (CRS). CRS serves as nonpartisan
shared staff to congressional committees and Members of Congress. It operates solely at the behest of and
under the direction of Congress. Information in a CRS Report should n ot be relied upon for purposes other
than public understanding of information that has been provided by CRS to Members of Congress in
connection with CRS’s institutional role. CRS Reports, as a work of the United States Government, are not
subject to copyright protection in the United States. Any CRS Report may be reproduced and distributed in
its entirety without permission from CRS. However, as a CRS Report may include copyrighted images or
material from a third party, you may need to obtain the permission of the copyright holder if you wish to
copy or otherwise use copyrighted material.

Congressional Research Service
R45951 · VERSION 3 · UPDATED
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