Difference between revisions of "Neutral redistricting criteria"

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Neutral criteria typically divide into two categories. One set of criteria are based solely on geography and demographic data. The other set depends on political data.
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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.
  
  
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== Population Equality ==
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== Demographic Criteria ==
  
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Demographic criteria include [[population equality]] and [[minority representation]]. [[Communities of interest]] can also be a demographic criterion.
  
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The most important piece of demographic data is the population. The goal is to have districts with nearly equal populations. For a state with ''k'' districts and a total population ''P'', the '''quota''' for each district is ''P/k''.
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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).
  
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Ideally each district should have a population as close as possible to the total population. In order to achieve other geographic goals, it may be necessary to have small variations from the quota. One measure is the '''range''', which is the difference between the largest and smallest district expressed as a percentage of the quota. State and federal laws limit the size of the range, and it can vary for different types of districts, for example state legislative districts may permit a larger range than congressional districts.
 
  
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Another measure is the '''maximum deviation'''. This is the maximum absolute percentage difference permitted for a district from the quota. This is generally set by state or federal law, and may be set at half the maximum permitted range if range is the appropriate legal standard.
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== Geographic Criteria ==
  
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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.
  
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== Contiguity ==
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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.
  
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The most important geographic condition for districts is that they be contiguous. In its simplest form this means that all areas in the district touch the same area, that is there are no separate pieces that make up the district. The idea of dividing a large area into smaller contiguous pieces allows redistricting to be translated into a problem in [[graph theory]].  
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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.
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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.
  
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Some states place restrictions on contiguity. The most common restriction is to bar point contiguity. point contiguity exists when an area of the district touches the rest of the district at only a single point. Two same-colored squares that are adjacent on a diagonal of a checkerboard are point contiguous.
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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.
  
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States can also require that it be convenient to travel within a district. This requires knowledge of the roads in the state. For example there can be a requirement that all areas of the district be reachable from each other by road. Roads can be limited to public roads, all season roads, and can include ferries. Use of major highways to link larger areas of a district can also encourage districts that represent [[communities of interest]].
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== Political Criteria ==
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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.
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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.

Latest revision as of 14:09, 13 August 2016

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.

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