American Community Survey (ACS): A survey that provides data in four categories every year. The categories are: social, demographic, economic and housing. The ACS replaced the ‘long form’ of the census that was collected once every 10 years. The ACS does not report counts of the population but rather estimates.
At-Large Election: In a jurisdiction (for example a city) with an at-large election system, all voters in the jurisdiction vote for all candidates running for office in that city. In at-large election systems, the candidates and office holders may live anywhere within the jurisdiction.
Census Block: The smallest level of census geography used by the Census Bureau to report census data. In urban areas, census blocks usually conform to city blocks, and in rural areas they are formed by other physical features and legal boundaries such as bodies of water and roads. Districting is based on census block level data.
Census Tract: A small, relatively permanent statistical subdivision of a metropolitan statistical area or selected non-metropolitan county, delineated for the purpose of presenting decennial census data. Census tracts usually contain between 2,500 and 8,000 people. Census tracts may be split by any sub-county geographic entity.
Citizen Voting Age Population (CVAP): A variable collected by the American Community Survey that is used in Voting Rights Act assessments. The population that is 18 years and older and a citizen of the United States.
Community of Interest: Group of people with one or more specific common interest. For districting, communities of interest are defined geographically based on where people with common interests live.
Compactness: Compactness often refers to a district’s shape and contours, focusing on how closely a district’s borders resemble a circle or square. When a district has ‘tentacles’ or oddly shaped borders, it is often said to be non-compact.
Contiguous OR Contiguity: A contiguous district is one in which all parts are geographically connected to each other in some way. Within a contiguous district, one may travel from any location to any other location without crossing the district boundary. Some districts are “water-contiguous” which usually means that islands have to be connected to the mainland; others are contiguous via a bridge. Drawing contiguous districts is applying the criterion of ‘contiguity.’
Cracking: A term used in Voting Rights that describes splitting significantly sized racial or ethnic communities into multiple districts, rather than keeping them together. Cracking is a particular problem when the division prevents the community from electing a candidate of its choice because it constitutes too small a portion of the electorate in the multiple districts.
Criteria for Districting: Rules established in the law that the districting body must follow when drawing electoral district boundaries. For example, one criterion is that districts have reasonably equal populations.
Deviation: The difference between the total population of the district and the ideal population of the district.
Districting: The process of creating equally populated electoral districts by using various criteria (such as Communities of Interest). In districting, electoral districts are created “from scratch” in a jurisdiction (a city for example) that does not currently have districts. Jurisdictions that do not have districts have “at-large” elections. Jurisdiction with districts redraw or adjust them (usually) every ten years after the release of the new census data to equalize the populations again. That process is called redistricting.
Equivalency File: A GIS file that shows the relationship between two geographic units. In districting, this file usually lists each census block in the dataset and indicates which district each block belongs to. The collection of block assignments is read by GIS software and displayed as district lines.
Geographic Information Systems (GIS) Software: A computer program for capturing, storing, checking, integrating, manipulating, analyzing and displaying data related to positions on the Earth’s surface. Examples of commonly used GIS software include Google Earth, ArcGIS, Maptitude and MapInfo.
Ideal Population: The total population for the jurisdiction as reported by the Census P.L 94-171 dataset divided by the number of districts. The ideal population is the number of people that each district should contain when the districting process is complete.
Map layer(s): GIS term for spatial/geographic data files as they are displayed by GIS software. Map layers may display attribute data. The term ‘map layer’ is sometimes used interchangeably with ‘spatial file’ and ‘GIS data file.’
Packing: A term used in Voting Rights that describes over-concentrating a significantly sized racial or ethnic community within one district when it could have been allocated between two or more districts in which it had the ability to elect a candidate of its choice. Packing is a problem because over-concentrating a community in one district reduces or dilutes its ability to achieve fair representation in the legislative body in general.
Racially polarized voting (RPV) or racial bloc voting or simply ‘polarized voting’: Racially polarized voting occurs when voters of different races tend to vote for different candidates. For example, in an area where White voters tend to vote against the candidates for which Asian American voters cast their ballots, racially polarized voting is present.
Reasonably Equal Population: The districting criterion that implements the one-person, one-vote concept derived from the 14th Amendment to the US Constitution.
Redistricting: The constitutionally mandated redrawing of local, state, and federal political boundaries every ten years following the U.S. census. Redistricting is done to equalize the populations in the districts, using various criteria.
Redistricting Data (P.L. 94-171) Summary File OR ‘P.L. 94-171 Summary File’: The official name of the file that contains data used for districting and redistricting. Creation of this file, using data collected through the Decennial Census was mandated by Public Law 94-171. The P.L. 94-171 file reports basic demographic data for all people in the U.S. and is released on the census block level.
Section 2 (of the Voting Rights Act): Section 2 of the Voting Rights Act (VRA) prohibits voting practices, policies, or procedures that have a discriminatory purpose or effect on racial or language minorities; this section applies nationwide and is a permanent provision of the VRA. To be in compliance with Section 2 of the VRA districts must provide voters with an equal opportunity to elect candidates of their choice.
Total Deviation: The sum of the combined deviations of all districts.
Voting Age Population (VAP): The number of people age 18 years or older.
Voting Rights Act (VRA): The Voting Rights Act (VRA) was originally passed in 1965 to prohibit discrimination on the basis of race or color. It has been amended several times, and now also prohibits discrimination based on membership in certain language minority groups.