Alternative Population Base

A count other than total population from the federal decennial census that is used for redistricting.


After each Decennial Census, the population count of the United States and overseas military and civilian dependents is used to calculate the number of representatives beyond the one per state to which each state is entitled. With 435 members of Congress, this effort disperses the remaining 385 representatives based on the method of equal proportions. The method of equal proportions is applied to the population totals for states (and overseas military) and does not include the Commonwealth of Puerto Rico, the Island Territories, or the District of Columbia. By law, the re-distribution of Congressional seats is required no later than December 31, following the collection of the Census or in years ending in 0. Due to delays in the 2020 Decennial Census associated with the COVID-19 pandemic, the most recent apportionment was not completed until April 26, 2021.

Apportionment Population

The population counts used to calculate the apportionment of the U.S. House of Representatives every 10 years using the results of the census. It consists of the total resident population (citizens and non-citizens) of the 50 states. In the 2020 Census, the apportionment population also included U.S. Armed Forces personnel and federal civilian employees stationed outside the United States (and their dependents living with them) that could be allocated, based on administrative records, back to a home state. This is the same procedure used in 1990, 2000, and 2010. Private U.S. citizens living abroad, who are not employed by the federal government, are not included in the overseas counts for apportionment.


When a district elects more than one member, all candidates run against each other on one ballot, and they are elected by the whole population of the district.


The survey of the U.S. population that occurs in the first year of every decade. The U.S. Constitution charges Congress with counting every person via the census enumeration, including citizens, children, and undocumented persons. Data from the census is used to determine the number of congressional seats each state receives during reapportionment and it has traditionally been used to ensure that districts have equal population and for compliance with other legal requirements such as the Voting Rights Act. The Census Bureau is the government agency that administers the census.

Census Bureau

The U.S. Census Bureau, which is part of the Department of Commerce, conducts the Decennial Census of Population and Housing as well as numerous ongoing projects for the federal government. The Bureau’s mission is to “Count Everyone Once, Only Once and in the Right Place” in the decennial census.

Coalition District

Electoral districts containing two minority groups which individually would not meet the criteria as to require the construction of a majority-minority district under Section 2 of the Voting Rights Act, but which do meet those criteria when combined as a coalition. (See Bartlett v. Strickland)


A constitutionally or statutorily created entity that some states use to draw district boundaries after a census.

  • Advisory Commission – A commission that draws a map for consideration by another body such as a legislature. Unlike other commissions, an advisory commission does not have the legal power to pass a binding map. The membership of an advisory commission may consist of legislators, non-legislators, or a mix. Five states currently use an advisory commission for legislative plans and three states currently use an advisory commission for congressional plans.
  • Backup Commission – A commission that draws plans only if the legislature cannot agree on a map or if the governor vetoes a proposal and no new map is passed. Five states currently use a backup commission for legislative plans and three states use a backup commission for congressional plans. The composition of backup commission varies by state. In Texas and Mississippi, for example, the backup commission is made up of specified statewide officials. Members of the legislature form the backup commission in Connecticut, Illinois, and Oklahoma.  
  • Independent Commission – A commission composed of individuals who are neither legislators nor other public officials and who are selected after a screening process conducted by an independent entity. An independent commission is comprised of citizens who have submitted applications and whose names are randomly drawn until all positions are filled.  Legislators may not serve on the commission. Two states currently use an independent commission for both legislative plans and congressional plans.
  • Political Appointee Commission – A commission composed, in whole or in part, of individuals who are directly appointed by elected officials or party leadership. In some states, the membership of a political appointee commission is evenly divided between parties but, in other states, there could be more members of one party than the other. Nine states currently use a political appointee commission for legislative plans and four states currently use a political appointee commission for congressional plans.
  • Politician Commission – A commission composed entirely of lawmakers or other elected officials. Politician commissions usually are appointed by the legislative or party leadership, the governor, or the chief justice of the state supreme court. Two states currently use a politician commission for legislative plans and no state currently uses one for congressional plans. 

Communities of Interest

A few states require districting plans to make an effort to preserve communities of interest. A community of interest refers to a group of people who are likely to have common legislative concerns and might benefit from collective representation in the legislature. Communities of interest may be defined by racial and ethnic demographics, economic opportunities, and/or geographic region. Other criteria such as following county, city, and town boundaries could be proxies for recognizing communities of interest. Relationships with a political party, incumbent, or candidate are sometimes excluded from this definition.


Describes a district having the minimum distance between all the parts of its constituency (a circle, square or a hexagon are examples of very compact district). Many states require that districts be compact, but few states actually define what exactly compactness means. Exceptions are states like Iowa that define compactness by particular statistical measures.

Congressional District

An area established by law for the election of representatives to the United States Congress. After the reapportionment of congressional seats among the states based on the decennial census population counts, each state with multiple seats is responsible for establishing CDs for the purpose of electing representatives. Each CD is to be as equal in population to all other CDs in the state as practicable, based on the decennial census counts. The boundaries may be changed more than once during a decade, unless otherwise provided by state law. The District of Columbia, Puerto Rico, and each Island Area each contain one CD for a single nonvoting delegate.


States commonly impose a requirement of contiguity. Contiguity means that the boundaries of a district are a single, uninterrupted shape; a person should be able to travel across a district without crossing into another district. Some states have specific provisions for special circumstances, such as for districting across water and islands.

Citizen Population (CPOP)

The total number of U.S. citizens enumerated within a census block or other geographic area; can be used for reapportionment.

Citizenship Status

People who indicate that they were born in the United States, Puerto Rico, a U.S. Island Territory, or abroad to at least one U.S. citizen parent are U.S. citizens. People who indicate that they are U.S. citizens through naturalization are also U.S. citizens. Naturalized U.S. citizens are foreign-born people who identify themselves as naturalized. Naturalization is the conferring, by any means, of citizenship upon a person after birth.

Components of Population Change

Demographic events (births, deaths, domestic migration, and international migration) used to estimate changes in the population during a specified time period.


A form of gerrymandering in which election districts are drawn in such a way that voters likely to support the opposing party are spread among multiple districts to dilute the power of their votes.

Crossover Districts

Districts where a minority group does not make up a majority of the population, but where the majority group votes sufficiently similar to the minority group so as to allow the minority’s preferred candidate to win the election.


The boundaries that define the constituency from which a public official is elected.

Effective Minority District

A district that allows minority voters therein to elect its preferred candidate of choice.


To ascertain the number of.


The U.S. Census Bureau adheres to the U.S. Office of Management and Budget’s (OMB) definition of ethnicity. There are two minimum categories for ethnicity: Hispanic or Latino, and Not Hispanic or Latino. OMB considers race and Hispanic origin to be two separate and distinct concepts. Hispanics and Latinos may be of any race.

Field Representative

A Census Bureau employee who interviews people to obtain information for a census or survey.


The practice of dividing or arranging a territorial unit into election districts in a way that gives one political party or voting group an unfair advantage in elections.

  • Racial Gerrymandering – Using racial demographics to group minorities together for the purpose of diluting their election power.
  • Partisan Gerrymandering – Using party-affiliation data and trends to knowingly advantage or disadvantage candidates from one political party in elections.

Ideal Population

The total population figure for the state or top-level jurisdiction divided by the number of seats in a specific legislative body.


A method of decennial census data collection used in some of the more remote, sparsely populated areas of the United States and the Island Territories where many of the households do not have mail delivery to city-style addresses. Enumerators list the residential addresses within their assignment areas on blank address register pages, mark the location of the residential structures on Census Bureau maps and conduct an interview for each household.

Legislative Body

Any entity that performs governmental legislative duties and whose membership is elected by the people; a.k.a. representational body.

Majority-Minority Districts

Term used by courts for electoral districts where a group or a single racial or language minority constitutes a majority (>50%) of the population. (These are also referred to as “effective districts.”)

Metes and Bounds

A detailed and very specialized description of district boundaries using specific geographic features and street directions as are usually used in describing real property for legal purposes.

Minority Opportunity District

A district with less than a 50 percent minority citizen voting age population but in which the minority group can still elect their candidate of choice.

Multimember District

A single district that elects two or more members to a legislative body.

Nested Senate and House Districts

A few states require the geographic boundaries of two or more house districts to be contained within senate districts. Nesting can be accomplished by drawing house districts, and consolidating those boundaries to form senate districts, or by establishing senate districts first and dividing those boundaries into house districts.

Numeric Population Change

Numeric population change is the difference between the population of an area at the beginning and end of a given time period.

One Person, One Vote

A constitutional standard established by the U.S. Supreme Court that mandates all electoral districts for representational bodies should be approximately equal in population. The degree of equality required may vary in congressional plans vs legislative/local plans.


A form of gerrymandering in which election districts are drawn in such a way that voters likely to support the opposing party are concentrated into a single district to limit the influence of their votes in other districts.


A set of boundaries for all districts of a representational body; a.k.a. map.


The margin by which the votes for the winning candidate exceeds the votes for the losing candidate with the highest number of votes; if the winner receives more than 50% of the total votes they win with a majority, otherwise they win with a plurality.

Political Boundaries

States commonly require that districts minimize the splitting of counties, cities, towns or wards. Similar to contiguity, states may provide specific guidelines for how to split these boundaries if necessary to achieve other goals.


All people, male and female, child and adult, living in a given geographic area.


Preclearance is defined as the process of seeking the U.S. Department of Justice’s or the Washington D.C. Federal District Court’s approval for all changes related to voting. The VRA requires that areas with a history of voting discrimination and low turnout submit and receive approval for any voting change, including redistricting, before implementing the change. This process was designed to reduce discrimination, to increase voter turnout, and to ensure that each and every citizen has equal power to elect their preferred representatives. Preclearance is no longer required following the U.S. Supreme Court’s 2013 decision in Shelby County v. Holder.

Priority Value (PV)

A value calculated from a state’s apportionment population and from the number of its next potential seat in the U.S. House of Representatives (starting with the second seat, as each state automatically gets one); to determine apportionment, the PVs from all states are ranked in descending order, and the state with the largest PV is assigned the next seat until the last (435th) seat has been filled.


The U.S. Census Bureau collects race data through the census’s questions on racial self-identification in accordance with guidelines provided by the U.S. Office of Management and Budget (OMB). The racial categories included in the census questionnaire generally reflect a social definition of race recognized in this country and does not attempt to define race biologically, anthropologically, or genetically. In addition, it is recognized that the categories of the race question include race and national origin or sociocultural groups. OMB requires that race data be collected for a minimum of five groups: White; Black or African American; American Indian or Alaska Native; Asian; and Native Hawaiian or other Pacific Islander. OMB permits the Census Bureau to also use a sixth category - Some Other Race. Respondents may report more than one race.


Reapportionment has two meanings. First, it refers to the constitutionally required act of redistributing seats in Congress based on each state’s proportion of the nation’s population following the decennial census. Secondly, some states, use reapportionment as a synonym for redistricting.


The act of redrawing lines for electoral districts every ten years after the census in order to ensure that districts have equal population and comply with other legal requirements. States redistrict congressional and legislative boundaries, and many local governments, such as cities, counties, and school boards also redraw local electoral district boundaries every ten years. Redistricting is sometimes referred to as reapportionment.

Resident Population

The resident population of the United States includes persons residing in the 50 States and the District of Columbia. An area's resident population consists of those persons "usually resident" in that particular area (where they live and sleep most of the time). The resident population excludes people whose usual residence is outside of the United States, such as the U.S. military and federal civilian personnel living overseas (and their dependents living with them), as well as private U.S. citizens living overseas. The resident population also excludes residents of the Commonwealth of Puerto Rico, and residents of the island areas under United States sovereignty or jurisdiction (principally American Samoa, Guam, the Virgin Islands of the United States, and the Commonwealth of the Northern Mariana Islands.)

Resident Population Plus Armed Forces

All U.S. residents and members of the Armed Forces on active duty stationed outside the United States. This population does not include military dependents or other U.S. citizens living abroad.


For the purpose of Census Bureau surveys and the decennial census, sex refers to a person’s biological sex.

Single-Member District

District electing only one representative; in the U.S. House, states that are only apportioned the constitutional minimum of one seat are now frequently referred to as at-large states.

Single-Member Election

Election in which only one candidate is elected. While this is how all elections are held in single-member districts, it can also occur in multi-member districts if seats within the district are uniquely designated and not all are elected at the same time.

State Legislative Districts

An area from which members are elected to state legislatures. The SLDs embody the upper (senate) and lower (house) chambers of the state legislature. (Nebraska has a unicameral legislature and the District of Columbia has a single council, both of which are represented as an upper chamber legislative entity.)

State-Level Criteria

The legal requirements which a state must follow when drawing district lines. In some instances, states will list these conditions in a ranked order, requiring high-priority criteria to be satisfied before other standards. Most states, however, list these principles without a ranked order of priority. Some states include instructions to follow specific guidelines “where practicable,” signaling that specific criteria should be considered only when feasible amongst the other criteria.

Total Population (TPOP)

The total number of residents in a geographic area as enumerated by the census; most commonly used for reapportionment.


One political party holds the governorship, a majority in the state senate, and a majority in the state house in a state's government.


Occurs when the entirety of the population is not enumerated at the time of the decennial census and can lead to incomplete reapportionment and redistricting data (malapportionment).

Voting Age Population (VAP)

The number of persons 18 years of age and over.

Voting Tabulation District (VTD)

A census term for a geographic area, such as an election precinct, where election information and data are collected; boundaries are provided to the Census Bureau by the states. Since boundaries must coincide with census blocks, VTD boundaries may not be the same as the election precinct and may include more than one precinct.

VRA: Voting Rights Act

  • Section 2 of the Voting Rights Act (VRA) – Part of the VRA that protects racial and language minorities from discrimination by a state, or other political subdivision, in voting practices.
  • Section 5 of the Voting Rights Act (VRA) – Part of the VRA that requires certain “covered” states and localities to pre-clear all election law changes with the U.S. Department of Justice or the federal district court for the District of Columbia before those laws take effect. The provision has become limited in scope since the 2013 decision in Shelby County v. Holder, where the U.S. Supreme Court invalidated Section 4(b), which provides the formula determining what jurisdictions were subject to this section. This decision effectively suspended Section 5 of the VRA.

Definitions were compiled from the Census Bureau Glossary, NCSL, National Geographic, ESRI, and the Education Glossary. All terms are linked to their respective source.