Redistricting has an impact on every American voter, but is often an opaque process with an insiders' vocabulary that can be a source of confusion for people who are unfamiliar with redistricting language. Using pre-existing sources like the Texas Legislative Council, NCSL, Redistricting the Nation and Louisiana's Redistricting, along with our own analysis, here is a guide to key terms frequently used within the redistricting community.
To see the definitions that the other organizations use please follow the links below:
Alternative Population Base: Population count other than the official census data that is used for redistricting. One example of an alternative population base is "voting age population."
Alternative voting system: See "proportional voting"
American Community Survey (ACS): Ongoing census survey sent to a sample of three million housing units annually. The ACS collects detailed demographic and socioeconomic population and housing characteristics, similar to the information collected on the former long form census questionnaire. The data is collected continuously rather than once a decade, so the ACS provides more current data.
Area dispersion: Measurement comparing the relative degree to which a district's area is compact with the area of a similar compact figure. It is the ratio of the area of the district to the area of the smallest convex polygon that can enclose the district. [See "compactness".]
Assignment unit: Unit of geography that may be used as a building block to draw a redistricting plan.
Bailout: The power jurisdictions covered by Section Five of the Voting Rights Act have to seek their permanent removal from preclearance requirements.
Candidate of choice: The candidate favored by a like-minded group of racial minority voters in a district. The Voting Rights Act requires that certain minority groups be given enough numbers in a district so that the minority group has the ability to elect their own candidate of choice without being continually outvoted by racial/ethnic majorities.
Census: Process of surveying and counting the U.S. population, using mailed surveys and in-person visits to homes, mandated by the U.S. Constitution and done every ten years by the federal government. Its results are used for reapportioning House seats among the states and redistricting districts within states. The last Census took place in 2010.
Census block: Smallest unit of census geography for which population data are counted and reported. Census blocks are delineated by the Census Bureau and are generally bounded by physical features such as roads, creeks, or shorelines, but also may be bounded by invisible features such as city, county, school district, or voting precinct boundaries. Census blocks are generally between 30,000ft² and 40,000ft².
Census block group: Subdivision of a census tract composed of a group of contiguous census blocks.
Census Bureau: Government agency that is responsible for the United States Census. It also gathers other national demographic and economic data. As part of the United States Department of Commerce, the Census Bureau serves as a leading source of data about America's people and economy.
Census Designated Place (CDP): Densely settled, unincorporated area locally identified by a name, such as an unincorporated town, for which the Census Bureau reports population. The boundaries of a census designated place are established by the Census Bureau in cooperation with state and local government officials.
Census tract: Set of block groups combined to create a unit of census geography delineated by local committees in accordance with census bureau guidelines for the purpose of collecting and presenting decennial census data.
Choice voting: A form of proportional representation (PR) that is used in some American elections and is widely used for local and some national elections in democracies such as Australia, Ireland, Malta and United Kingdom. Under choice voting, like-minded representatives win seats in multi-seat districts in proportion to their share of voting support. Choice voting also assures that political parties or candidates will gain the percentage of legislative seats that reflects their public support. Choice voting is also called "single transferable vote'' and "preference voting."
Citizen Voting Age Population CVAP: Number of persons in a geographic unit who are citizens and at least 18 years of age.
Community of interest (COI): Group of people in a geographical area, such as a specific region or neighborhood, who have common political, social, or economic interests. Examples of COI's are groups who are committed to preserving a local park, creating a new subway line in a city or achieving increased funding for a community college.
Compactness: Minimizing the distance between all parts of a district. There are many types of compactness measures including: area dispersion and perimeter.
Contiguity: A district that is within one continuous boundary and whose parts all touch one another at more than a point. All districts in the United States must be contiguous, however, some districts stretch the limits of this requirement by connecting different landmasses through water or having two districts intersect at a single point that takes up no area.
County lines: The boundary between counties within a state. Splitting counties between districts is prohibited in certain states when it is possible to keep them intact.
Cracking: Splitting a like-minded voting group's electoral strength by dividing its population into multiple districts.
Cumulative voting: A semi-proportional voting system used in about seventy American jurisdictions in which voters cast as many votes as there are seats. But unlike winner-take-all systems, voters are not limited to giving only one vote to a candidate. Instead, they can put multiple votes on one or more candidates. For instance, in an election for a five-seat body, voters could choose to give one vote each to five candidates, two votes to one candidate and three to another, or all five votes to a single candidate. If members of a minority group work together and get behind a single candidate, "plumping" all of their votes on him or her, they can hope to elect that candidate, even if they only make up a minority share of the population.
Department of Justice (DOJ): Department within the federal government's executive branch which ensures that federal law is followed and prosecutes offenders when it is not. The DOJ has a Voting Section that monitors state election law and enforces the Voting Rights Act.
Deviation: Amount or percentage by which a district's population varies from that district's ideal population.
Dilution: Reduction in the voting strength of a particular group resulting from redistricting and use of winner-take-all elections. The phrase "minority vote dilution" describes racial minorities being in a position of not being able to elect candidates of choice.
District: Boundaries that define the constituency of an elected official. A district can include one or more elected legislators.
Fourteenth Amendment to the U.S. Constitution: Provision of the U.S. Constitution that includes the Equal Protection Clause, which prohibits the states from denying persons equal protection of the law. The Equal Protection Clause is the primary basis of the one-person, one-vote principle, which courts in redistricting cases have defined to mean equality of population (including non-eligible voters) in districts.
Fifteenth Amendment to the U.S. Constitution: Provision of the U.S. Constitution that prohibits the right to vote from being denied or abridged on account of race.
Gerrymander: Drawing a district with boundaries that favor one or more groups of voters and/or some candidates over others.
Partisan gerrymandering: Drawing a district to favor one political party over others.
Racial gerrymandering: Drawing a district to favor one racial group over others.
Ideal district population: Number of people that should be in each of a jurisdiction's districts. This number is calculated by dividing the total population of the jurisdiction by the number of districts being created. The number can vary if other measures are used such as voting age population, citizens voting age population and registered voters.
Incumbent protection: Drawing a district to aid the incumbent with reelection. [See "gerrymandering."]
Influence district: A district in which a racial minority does not have the ability to elect a candidate of choice, but makes up a substantial number of voters with the theoretical power to influence who wins the election.
Like-minded voters: Voters who by nature of their race, ethnicity, partisan affiliation, political philosophy or some other characteristic tend to vote for the same candidate.
Limited voting: A semi-proportional voting method used in several dozen U.S. jurisdictions in which oters cast fewer votes than there are seats to be elected, thereby allowing a majority group to control the majority of seats, but not all seats. The greater the difference between the number of seats and the number of votes, the greater the opportunities for fair representation.
Majority-minority district: District where a minority group composes a majority of the population. Also can be called "minority opportunity districts."
Method of equal proportions: Mathematical formula prescribed by federal statute that is used to reapportion congressional seats among the states after each decennial census.
Multi-member district: A district that elects more than one member to a legislature. Used for legislative elections in several states and thousands of local elections, although the number of legislators elected from multi-member districts has declined sharply over the past century.
Nesting: Redistricting method of creating two or more state lower legislative chamber districts that are completely contained within the boundaries of a state upper legislative chamber district.
One person, one vote: Constitutional principle based on Article I, Section 2 and the 14th Amendment which holds that each person's vote should count the same as every other person's vote. Under this principle each district within a jurisdiction should have the same or substantially the same population. This definition in fact suggests a right to districts with equal number of constituents rather than a right to districts with an equal number of voters. The standard for exact population equality is very strict for congressional districts, but less so for state and local government, with 10% population deviations permitted in state legislative districting.
P.L. (Public Law) 94-171: 1975 federal law that requires the U.S. Census Bureau to provide, each state with Census data that the states will need for redistricting. This data is typically provided by April 1st of each year following the completion of a census.
P.L. (Public Law) 105-119: 1997 federal law that requires the U.S. Census Bureau to make census data available to the public. This data is typically provided early in the year after the census is completed.
Packing: Consolidating a minority group's population into one district to give it more representation than is needed to create a majority in that district while reducing its presence, and electoral influence, in surrounding districts.
Perimeter: Ratio of the area of the district to the area of a circle with the same perimeter as the district. [See "compactness."]
Plurality: A percentage of votes that, although not being the majority, is the winning total because it is higher than all than any other candidate in an election received. (Sometimes inaccurately called "first past the post," but there is no "post" or minimum level of support necessary to win.)
Polarization: Elections in which substantial grouping of voters in a district have overwhelmingly distinct preferences. Used when applied to racial group preferences as a condition for winning Section Two cases under the Voting Rights and often discussed in the context of distinct political preferences and concerns about excessive partisanship in legislatures.
Population: The total number of people, including noncitizens and children, who reside in a jurisdiction.
Preclearance: Review of a jurisdiction's redistricting plan by the U.S. Department of Justice or the U.S. District Court for the District of Columbia, clearing it as passing the standards set by Section 5 of the Voting Rights Act of 1965, as amended in 1982 and 2006. The preclearance process takes up to 60 days and if the DOJ objects to the change the state has three options: 1) accept the objection and modify its proposal; 2) as for a reconsideration; and 3) file suit in the U.S. District Court for the District of Columbia seeking a declaratory judgment that their proposal is valid under the VRA. The Department over time has precleared more than 99% of all preclearance requests.
Proportional voting: A non-winner-take-all voting method used to elect legislators in a district with more than one seat. "Proportionality" describes the ability of like-minded voters to elect candidates in proportion to their share of the vote, not any guaranteed outcomes for any particular group of voters.
Racially polarized voting/racial bloc voting: Circumstances where the voting preferences of a particular group consistently vary from the preferences of other groups. When a white majority consistently defeats the preferences of a racial minority that is protected under the Voting Rights Act, a jurisdiction may need to change its district plan and/or electoral structure under Section 2 of the Voting Rights Act.
Reapportionment: Process of redistributing the number of seats in a jurisdiction's legislative body to the districts of that jurisdiction based on the results of the latest Census. For example, due to particularly large population increases, Texas' congressional delegation will increase by four seats in 2012 while other states like New York and Michigan will lose seats following the 2010 reapportionment.
Redistricting: Process of redrawing the districts within a jurisdiction to reflect the results of the reapportioning process as well as the results of the Census; for example, congressional district boundaries may be changed to account for population shifts within a state.
Sampling: Method of measuring a part of a population and extrapolating out to determine the full population. This technique is not allowed for conducting the federal census.
Sections 2 and 5 of VRA: See "Voting Rights Act
Single-member district: A district that only elects one representative. Required for U.S. House district by a 1967 statute, not by the Constitution.
Submissions (VRA): Process that jurisdictions, which are covered by the VRA take in order to change their voting laws and district lines. The process requires the jurisdiction to submit any to the Department of Justice and gives the DOJ sixty days to review the new plan. The DOJ can object to the plan and the jurisdiction at that point has the option to accept the objection and modify the plan, ask for reconsideration or ask the District Court for the District of Columbia to overrule the DOJ.
Traditional districting principles: Term often used to refer to criteria, such as compactness and contiguity, which have historically been considered in drawing legislative or other districts.
Undercount: Error in Census data due to counting mistakes or inability to count some persons.
Voting age population (VAP): Number of persons in a geographic unit who are at least 18 years of age.
Voting Rights Act (VRA): Federal law prohibiting discrimination in voting practices on the basis of race or language group. [See also "Department of Justice"]
Section 2: Prohibits states and other jurisdictions from maintain voting laws, standards or practices that abridge the right to vote on the basis of race or language group. Covers all parts of the United States.
Section 5: Requires that jurisdictions that have been determined to violate Section 2 and placed on a watchlist receive preclearance from the U.S. Department of Justice or the District Court for the District of Columbia for any changes to districts or other voting laws. Section 5 covers nine states and portions of seven others.