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Glossary

American Community Survey (ACS)

An 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. Single-year estimates are available annually for geographic areas with a population of 65,000 or more. Three-year estimates are available annually for geographic areas with a population of 20,000 or more. In December 2010, the first five-year estimates at the census tract and block group level were made available.

Anglo

Those persons who identified their race on the census form as White only and not Hispanic.

Assignment unit

Any unit of geography that may be used as a building block to draw a redistricting plan. Assignment units available in RedAppl are counties, census tracts, census block groups, census blocks, and VTDs (voting tabulation districts).

Black

Those persons who identified their race on the census form as Black, African American, or Negro only or Black and any other race. Black persons can be either Hispanic or non-Hispanic.

Black + Hispanic

A combined population category that includes all persons who identified their race as Black and all persons who identified themselves as Hispanic. The total is adjusted so that those who indicated they were both Black and Hispanic are not counted twice. The category is frequently examined for redistricting purposes in areas in which Black and Hispanic voters may form political coalitions or vote together as a bloc.

Census block

The 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 nonvisible features such as city, county, school district, or voting precinct boundaries.

Census block group

A subdivision of a census tract composed of a group of contiguous census blocks with the same first digit of their four-digit census block member. Block groups generally contain between 600 and 3,000 people.

Census day

April 1, 2010. The date for which census data was collected.

Census Designated Place (CDP)

A 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

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. Census tracts are made up of block groups. Their boundaries generally follow visible features, though in some circumstances their boundaries may follow governmental unit boundaries or other nonvisible features. In general, census tracts contain between 1,200 and 8,000 people, with an optimum population size of 4,000.

Community of interest

A term sometimes used to describe a grouping of people in a geographical area, such as a specific region or neighborhood, who have common political, social, or economic interests.

Compactness

Three basic types of compactness measures are used to analyze the area, perimeter, and population of a district. More than 36 different variations on these compactness measures exist. No single measure of compactness is recognized as the "best" measure. The measures presented in RedAppl and on reports have a range from zero to one, with one indicating perfect compactness for the particular scale. The lower the score, the less compact the district.
  • Types of Compactness Measures:
    • Area Dispersion: This measure examines the relative degree to which a district's area is compact when compared 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 (imagine a rubber band stretched around the district). A district in the shape of a square would receive a perfect score of one using this measure. This measure penalizes a district that has long "fingers" or extensions, making it less compact because it requires a larger convex polygon to enclose the entire district, yet much of that polygon is empty.
    • Perimeter: This measure compares the relative length of the perimeter of a district to its area. It is the ratio of the area of the district to the area of a circle with the same perimeter as the district. A perimeter-to-area measure penalizes a district's compactness score whenever the boundaries are uneven or irregular: the more the boundary zigzags (for example, a river), the less compact the district using this measure.
    • Population: This is a population-based compactness measure computed as the ratio of the population of the district to the population of all census blocks contained in the smallest convex polygon enclosing the district. The greater the population within the convex polygon that is not within the district, the less compact the district under this measure.

Contiguity

Adjacency. For redistricting purposes, a district is considered to be contiguous if all parts of the district touch one another at more than a point, so that the entire district is within a continuous boundary. Legal standards governing redistricting for various governmental bodies often require all of the territory in each district to be contiguous.

County election precincts

Also called voting precincts. Geographic units established by county commissioners courts for the purpose of election administration. The voters in an election precinct usually vote at a single polling place, so the votes cast in the precinct may be counted separately from other precincts.

Deviation

The amount or percentage by which a district's population differs from the ideal district population for the particular district type.

DistrictViewer

A web application for viewing interactive maps of current Texas legislative, congressional, and SBOE districts and public redistricting plans over the Internet. Desktop version available at http://gis1.tlc.state.tx.us. Mobile version available at http://gis1.tlc.state.tx.us/dvrmobile.html.

Equal Protection Clause

See "Fourteenth Amendment to the U.S. Constitution."

Fourteenth Amendment to the U.S. Constitution

The 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.

Fifteenth Amendment to the U.S. Constitution

The provision of the U.S. Constitution that prohibits the right to vote from being denied or abridged on account of race.

Fragmentation

The division of members of a geographically concentrated group, such as a racial or political group, among different districts for the purpose of minimizing the group's voting strength.

Geographic Information System (GIS)

A graphics-based computer system that relates geographic features (such as census tracts, cities, VTDs, or counties) to data about those features (such as population, race, or voting behavior).

Gerrymander

(noun) A district or set of districts with unusual boundaries that is drawn to favor one or more interest groups over others; (verb) To draw a district or set of districts with unusual boundaries that favor one or more interest groups over others.

Hispanic

Those persons who identified themselves on the census form as Hispanic, Latino, or Spanish origin. Hispanic persons can be of any race.

Ideal district population

A measure calculated by dividing the total population of the state or other jurisdiction being redistricted by the number of districts in the legislative body or board being redistricted. For example, in 2010, the ideal district population for Texas Senate districts was 811,147, which is the 2010 state population (25,145,561) divided by the number of districts in the Texas Senate (31).

Legislative Redistricting Board (LRB)

The body responsible for adopting legislative redistricting plans if the legislature fails to enact such plans during the regular session following the publication of the decennial census. The board consists of the lieutenant governor, speaker of the house, attorney general, comptroller, and land commissioner. See Section 28, Article III, Texas Constitution.

Method of equal proportions

The mathematical formula prescribed by federal statute that is used to reapportion congressional seats among the states after each decennial census.

Minority vote dilutions

The creation of districts that either (1) divide members of a racial or ethnic minority group among several districts, artificially reducing the group's opportunity to influence elections (see "Fragmentation") or (2) place high percentages of members of a racial or ethnic minority group in one or more districts so that minority voting strength is artificially limited to those districts and is minimized in neighboring districts (see "Packing").

Non-suspense voter registration

see Voter Registration.

One person, one vote

The principle that each person's vote should count the same as every other person's vote; it is achieved by the allocation of the same or substantially the same population to each district of a particular type, such as a congressional district. The courts derive the one-person, one-vote standard primarily from the Equal Protection Clause of the Fourteenth Amendment to the U.S. Constitution. For congressional districts, the one-person, one-vote requirement also derives from Section 2, Article I, and from Section 2 of the Fourteenth Amendment to the U.S. Constitution.

Other

Those persons who did not identify themselves on the census form as White only, Black, or Hispanic.

P.L. (Public Law) 94-171

The federal statute that requires the census bureau to provide, by April 1 of each year following a decennial census, the census data necessary for redistricting.

P.L. (Public Law) 105-119

The 1997 federal statute that requires the Census Bureau to make publicly available the census data resulting from the actual responses to the census forms and follow-up efforts, without any statistical adjustments to correct for overcounts and undercounts.

Packing

Creating a district with an unnecessarily high concentration of a particular group of voters, such as a racial or political group, which tends to result in the election of the group's candidate of choice in any election in that district while diluting the group's voting strength in neighboring districts due to the "wasting" of votes in the packed district.

Population estimates

An approximation of the population of a geographic unit at a point in the past or present for which an actual population count is not available.

Population projections

An approximation of the population of a geographic unit at a point in the future based on specific assumptions regarding future demographic trends in the geographic unit.

Preclearance

Approval under Section 5 of the Voting Rights Act of 1965 of a redistricting plan or other change in state or local election procedures by a special three-judge federal district court in Washington, D.C., or by the U.S. Department of Justice.

Public plan

A redistricting proposal that has been made public through the legislative process or otherwise publicly released by its author.

Racially polarized voting

The term used to describe circumstances in which the voting preferences of a racial or ethnic group consistently vary from those of other racial or ethnic groups, particularly when the different voting preferences are based on the race of the candidate. Also referred to as "racial bloc voting."

Reapportionment

Reallocation of a fixed number of seats in a governmental body among established political units. Following each decennial census, the seats in the U.S. House of Representatives are reapportioned among the states. The result is that each state is assigned its number of congressional seats for the next decade. Reapportionment does not redefine district boundaries. The term is sometimes used imprecisely to mean "redistricting."

RedAppl

The Texas Legislature's geographic information system (GIS) application developed by the Texas Legislative Council used for redistricting.

Redistricting

The process of redefining the geographic boundaries of individual election units, such as legislative or congressional districts or county election precincts.

Retrogression

The term used to describe a reduction in the voting strength of a racial or ethnic group resulting from a redistricting plan or other change in election procedures. Retrogression is the primary test used for evaluating a change in election procedures for preclearance under Section 5 of the Voting Rights Act of 1965.

Spanish Surname Voter Registration (SSVR)

SSVR is reported by the secretary of state using a comparison of state voter registration records and the 1990 Census List of Spanish Surnames. No other estimate of Hispanic voter registration in Texas is available by precinct for the entire state. Most sources agree that the match between people who have Spanish surnames and those who consider themselves Hispanic is relatively good in Texas (the Census Bureau estimates a 90 percent correlation for the state).

Statistical sampling

The statistical method by which characteristics of a small group are measured and applied to the population as a whole.

TIGER (Topologically Integrated Geographic Encoding and Referencing System

The cartographic map database, prepared by the census bureau, that Texas will use as the geographic database for redistricting.

Total range of deviation

The range over which the populations of all districts in a redistricting plan deviate from the ideal district population, computed by examining the deviations of the most populous and least populous districts.

Traditional districting principles

A term often used to refer to criteria, such as compactness and contiguity, that have historically been considered in drawing legislative or other districts.

Undercount

The error in census data that results from the failure to count some persons or housing units in the decennial census. Historically, certain groups, such as members of racial or ethnic minorities, have been disproportionately undercounted by the federal census.

Voter registration

The number of persons registered to vote in a county. Total voter registration is the total number of all persons who are on a county's voter registration roll. Non-suspense voter registration is total voter registration minus the number of previously registered voters who fail to respond to a confirmation of residence notice sent by the county voter registrar.

Voting age population

The number of persons in a geographic unit who are at least 18 years of age. Because some population groups, such as racial or ethnic minorities, tend to be younger on average than the population as a whole, the voting age populations are frequently compared in evaluating the potential voting strength of those groups.

Voting Rights Act

The federal law prohibiting discrimination in voting practices on the basis of race or language group, codified as 42 U.S.C. Section 1973 et seq. The official title of the act is the Voting Rights Act of 1965. Sections 2 and 5 of the act are important for redistricting.
    • Section 2 Prohibits the adoption of voting standards or practices that abridge the right to vote on the basis of race or language group. This section applies to all states and other governmental units and may be used to challenge a redistricting plan that discriminates against a racial or language minority group.
    • Section 5 Requires that changes in election procedures (including changes in district lines) be precleared by the U.S. Department of Justice or by a three-judge federal district court in the District of Columbia before the changes are put into effect. Preclearance is granted only if the change is determined not to have the purpose or effect of denying or abridging the right to vote on the basis of race or language group. Only certain states, including Texas, and other jurisdictions are subject to Section 5.

Voting tabulation district (VTD)

The census geographic equivalent of a county election precinct, created for the purpose of relating election data to census data. VTDs can differ from actual election precincts because election precincts do not always follow census geography. During the approximation process that creates VTDs, county election precinct boundaries that do not follow census geography are assigned to the nearest census block boundary.

Who Represents Me?

The Texas Legislature's address matching system that identifies the member of the United States Congress, the Texas Senate, or the Texas House of Representatives who represents a user-entered location. Desktop version vailable at http://www.fyi.legis.state.tx.us. Mobile version available at http://gis1.tlc.state.tx.us/wrmmobile.html.

The Texas Legislative Council, a nonpartisan legislative service agency, provides technical and legal support to the Texas legislature for redistricting.