Neutral redistricting criteria

Redistricting criteria typically divide into categories based on the source of the information used for the criteria. Criteria based demographic and geographic information are generally neutral. Use of political data for redistricting is the traditional means to gerrymander. However, there are neutral political criteria as well. Compliance with the Voting Rights Act generally may require demographic, geographic and political data.

Demographic Criteria

Demographic criteria include population equality and minority representation. Communities of interest can also be a demographic criterion.

Demographic criteria can be derived from census data. The Census releases a data set called Redistricting Data (PL 94-171). This is limited data set in the range of information but it is tabulated at a very fine granularity. The 2010 Redistricting Data Summary File included the total population, voting age population (VAP) 18 and older, population by race, population by Hispanic identification, total housing units, and housing units by occupancy. Other economic and household data is based on the sampling done by the American Community Survey (ACS).

Geographic Criteria

Geographic Criteria include contiguity, compactness, and geographic integrity. Communities of interest can also be a geographic criterion, but as a geographic criterion it is usually handled by geographic integrity.

Geographic Criteria can be derived from census data. The Census has a number of different geographic units used to aggregate data. The smallest of these is the census block, which can correspond to a city block or a large rural area bounded by roads and other natural features. Census blocks are used to build other geographic units. Block groups represent 600-3000 people, and census tracts represent 1200-8000 people and are the statistical subdivisions of counties (or equivalent) for the Census.

Counties are also subdivided by 29 states into minor civil divisions. These MCDs are legal entities and can be governmental units like townships or electoral units like precincts that have generally fixed boundaries. Other states have census county divisions (CCD) which are statistical only.

Places are cities, villages, boroughs and towns. Some states nest places entirely within a county or MCD. Incorporated places are tabulated by the Census and Census designated places (CDP) are used for statistical areas associated with unincorporated places.

School districts are a significant subdivision in states and counties. The Census tracks demographic data in school districts, and the public may feel more affinity for the school district they are in than other subdivisions.

Political Criteria

Political criteria include partisan fairness, competitiveness and responsiveness. Political criteria are determined by considering the natural political inclination of a district as well as the state in which the district resides. One common mechanism used to assess political inclinations of a population is the PVI, short for the Partisan Voting Index.

The use of political criteria is hotly debated among redistricting reformers. Some feel that the redistricting process should be completely independent of political results, except when required to meet the federal Voting Rights Act. However, without political measures, there is the possibility of a plan that intentionally or inadvertently tilts towards one party. Even if a plan has no tilt, it can pack partisans into seats in such a way that neither party can effectively contest the seats held by the other party. That prevents the electorate from registering a shift in its opinion by means of their representative delegation.