Glossary of Terms


Following each census, the 435 seats in the United States House of Representatives are apportioned to each state based on state population. The larger the state population, the more congressional representatives the state will be apportioned. Apportionment, unlike redistricting, does not involve map drawing.

At-large election system

An at-large election system is one in which all voters can vote for all candidates running for open seats in the jurisdiction. In an at-large election system candidates run in an entire jurisdiction rather than from districts or wards within the area. For example, a city with three open city council positions where all candidates for the three seats run against each other and the top three receiving the most votes citywide are elected is an at-large election system. In at-large election systems, 50% of the voters control 100% of the seats. At-large election systems can have discriminatory effects on minorities where minority and majority voters consistently prefer different candidates and the majority will regularly defeat the choices of minority voters because of their numerical superiority.

Census block

The smallest level of census geography used by the Census Bureau to collect census data. Census blocks are formed by streets, roads, bodies of water, other physical features and legal boundaries shown on Census Bureau maps. Redistricting is based on census block level data.

Census tract

A level of census geography larger than a census block or census block group that usually corresponds to neighborhood boundaries and is composed of census blocks.

Community of interest

A community of interest is a neighborhood or community that would benefit from being maintained in a single district because of shared interests, views or characteristics.


A term used to describe the appearance of a district. Compactness refers to the overall shape of the district.


A term used to describe the appearance of a district. A geographically contiguous district is one in which all parts of the district are attached to each other.


A form of dilution occurring when districts are drawn so as to divide a geographically compact minority community into two or more districts. If the minority community is politically cohesive and could elect a preferred candidate if placed in one district but, due to cracking, the minority population is divided into two or more districts where it no longer has any electoral control or influence, the voting strength of the minority population is diluted.

Crossover Districts

A crossover district is one in which minorities do not form a numerical majority but still reliably control the outcome of the election with some non-minority voters crossing over to vote with the minority group.


The deviation is any amount of population that is less than or greater than the ideal population of a district. The law allows for some deviation in state and local redistricting plans. However, Congressional districts must not deviate too far from the ideal population. See below for definition of “ideal population.”


The drawing of electoral districts to give one group or party an unfair advantage over another.

Gingles Factors

The Gingles factors are three preconditions set forth by the U.S. Supreme Court in Thornburg v. Gingles, 478 U.S. 30 (1986), that a minority group must prove to establish a violation of Section 2 of the Voting Rights Act. These preconditions are the following: 1) a minority group must be sufficiently large and geographically compact to comprise a majority of the district; 2) the minority group must be politically cohesive (it must demonstrate a pattern of voting for the same candidates); and, 3) white voters vote sufficiently as a bloc usually to defeat the minority group’s preferred candidate.

Ideal population

The ideal population is the number of persons required for each district to have equal population. The ideal population for each district is obtained by taking the total population of the jurisdiction and dividing it by the total number of districts in the jurisdiction. For example, if a county’s population is 10,000 and there are five electoral districts, the ideal population for each district is 2,000.

Influence district

An influence district is one that includes a large number of minority voters but fewer than would allow the minority voters to control the election results when voting as a bloc. Minority voters are sufficient in number in “influence districts” to influence the outcome of the election.

Minority-coalition district

A minority-coalition district is a type of majority-minority district in which two or more minority groups combine to form a majority in a district. In most jurisdictions, minority-coalition districts are protected under Section 2 of the Voting Rights Act if the requirements set forth in Thornburg v. Gingles are satisfied.

Majority-minority district

A majority-minority district is one in which racial or ethnic minorities comprise a majority (50% plus 1 or more) of the population. A majority-minority district can contain more than one minority group. Thus, a district that is 40% Hispanic and 11% African American is a majority-minority district, but it is not a majority Hispanic district. This is also referred to as a minority coalition district. See definition of minority-coalition district.

Minority opportunity district

A minority opportunity district is one that provides minority voters with an equal opportunity to elect a candidate of their choice regardless of the racial composition of the district.

Minority vote dilution

Minority vote dilution occurs when minority voters are deprived of an equal opportunity to elect a candidate of choice. It is prohibited under the Voting Rights Act of 1965. Examples of minority vote dilution include cracking, packing and the discriminatory effects of at-large election systems.

Multimember district

A district that elects two or more members to office.

One-person, one-vote

A constitutional requirement that requires each district to be substantially equal in total population.


A form of vote dilution prohibited under the Voting Rights Act where a minority group is overconcentrated in a small number of districts. For example, packing can occur when the African American population is concentrated into one district where it makes up 90% of the district, instead of two districts where it could be 50% of each district.

PL 94-171

The federal law that requires the United States Census Bureau to provide states with data for use in redistricting and mandates that states define the census blocks to be used for collecting data.

Political subdivision

A division of a state, such as a county, city or town.


An area created by election officials to group voters for assignment to a designated polling place so that an election can be conducted. Precinct boundaries may change several times over the course of a decade.


Preclearance applies to jurisdictions that are covered under Section 5 of the Voting Rights Act. Preclearance refers to the process of seeking review and approval from either the United States Department of Justice or the federal court in the District of Columbia for any voting changes to a Section 5 covered jurisdiction. Redistricting plans in Section 5 covered jurisdictions must also receive preclearance.

Racially polarized voting or racial bloc voting

Racially polarized voting is a pattern of voting along racial lines where voters of the same race support the same candidate who is different from the candidate supported by voters of a different race.


Same as apportionment.


Redistricting refers to the process by which census data is used to redraw the lines and boundaries of electoral districts within a state to ensure that districts are substantially equal in population. This process affects districts at all levels of government – from local school boards, wards, and city councils to state legislatures and the U.S. House of Representatives.


A voting change to a Section 5 covered jurisdiction that puts minorities in a worse position under the new scheme than under the existing one.

Section 2 (of the Voting Rights Act)

A key provision of the Voting Rights Act that that protects minority voters from practices and procedures that deprive them of an effective vote because of their race, color or membership in a particular language minority group.

Section 5 (of the Voting Rights Act)

A key provision of the Voting Rights Act that prohibits jurisdictions covered by Section 5 from adopting voting changes, including redistricting plans, that worsen the position of minority voters or changes adopted with a discriminatory purpose. See preclearance.

Single-shot voting

Single-shot voting can be described as follows: “Consider a town of 600 whites and 400 blacks with an at-large election to choose four council members. Each voter is able to cast four votes. Suppose there are eight white candidates, with the votes of the whites split among them approximately equally, and one black candidate, with all the blacks voting for him and no one else. The result is that each white candidate receives about 300 votes and the black candidate receives 400 votes. The black has probably won a seat. This technique is called single-shot voting.” U.S. Commission on Civil Rights, The Voting Rights Act: Ten Years After, pp. 206-207 (1975).

Traditional redistricting principles

Traditional redistricting criteria applied by a state such as compactness, contiguity, respect for political subdivisions, respect for communities of interest, and protection of incumbents.


The number of Americans missed in the census.