Common Redistricting Criteria
After each decennial Census, governments at all levels (e.g. congressional, state legislative, municipal, county, special districts) adjust the districts of their respective legislative bodies to reflect the changing demographics of their region. The individual or group drawing the map must be given criteria on what they can and cannot do when creating a map. Redistricting processes and rules vary across states, so map-drawers must be aware of the laws of the state and jurisdiction to avoid having their maps rejected or deemed unconstitutional. Some states will strictly define what redistricting criteria must be followed while others will not. Some municipalities or jurisdictions will also have previously defined their own criteria. Other jurisdictions will be able to adopt their own criteria.
This document is not intended to be a legal guide, but simply a discussion of the most common redistricting criteria.
There are some criteria that are part of almost all redistricting guidelines:
- Equal Population — The population of each new district should be ‘equal’. When drawing congressional maps, court rulings have largely defined ‘equal’ as “within 1 person” based on the census’ latest PL 94-171 file. Unless state statute dictates otherwise, counties, municipalities and special districts are not required to adhere to such a strict definition, and districts can have differences within a small percentage of one another. Some states define the allowed deviations, otherwise the jurisdiction does it themselves. Some jurisdictions use as low as a 2% deviation, others as high as 10%. When you talk about percentages you also have to determine if this is an cumulative difference or individual district difference from the ideal population. An example would be a jurisdiction with a 5% deviation rule. A proposed map has one district with a -3% deviation (underpopulated) and another district with a positive 4% deviation (overpopulated). Under the rules is each district under a 5% cutoff and OK, or does the cumulative difference of 7% violate the rule?
- Contiguity — The district must be one cohesive unit. For example, you can’t draw one part of a district in the southeast corner of a county and add an unattached region in the northwest corner of the county. Those two sections will need to be physically linked. Definitions of contiguity can also vary between states, as some consider corner and point contiguity as part of the criteria, particularly in areas where geographic limitations (e.g. bodies of water) are present. There are of course sometimes areas which are not contiguous to the jurisdiction itself (examples would include physical islands or annexed pieces of land that do not touch the original jurisdiction), these of course cannot be drawn to be contiguous. https://redistricting.lls.edu/redistricting-101/where-are-the-lines-drawn/#contiguity
- Comply with the Federal Voting Rights Act — Section Two of the Federal Voting Rights Act prohibits discrimination on the basis of race, color, or membership in a language minority group. Generally speaking, it means existing majority-minority districts should be preserved and new majority-minority districts should be created where possible. Jurisdictions often use CVAP (Citizen Voting Age Population) data to determine minority percentages, and the allowed source data should be specified (CVAP vs VAP vs PL file demographics). At the federal level, a majority minority district must be 50% plus one additional person of the same protected class in one district. If a new majority minority district can be drawn in a “reasonably compact” way, it must be drawn. Section Five of the VRA required certain states and jurisdictions with a history of racial gerrymandering to submit their redistricting plans to the Department of Justice for preclearance, but this was struck down by the U.S. Supreme Court in 2013 (Shelby County v. Holder).
- Comply with State or Jurisdiction Voting Rights Laws – Federal VRA law is complicated, but largely dictates that a minority majority district consists of a single protected minority comprising more than 50% of the population, but state law or local jurisdiction law can go further than federal law. State law might favor the creation of ‘coalition districts’ where multiple minorities together can form a minority district. Additionally, states or jurisdictions can write Voting Rights Laws to not use a hard 50% cutoff, but rather use an “ability to elect” cutoff. This means if a district is 40% minority, but that 40% along with allied voters is large enough to see their ‘candidate of choice’ win, that can still be considered a minority district. Federal law, however, supersedes state and municipal law.
There are other criteria that are widely considered to be best practices:
- Use Practical Geographic Boundaries — This criteria means that, where possible, practical geographic boundaries should be used to create the lines of a district. This can include major roadways, municipal boundaries, waterways, park boundaries, school district boundaries, etc..
- Where Possible, Make Districts Compact — In terms of the overall shape, compactness refers to how closely packed together the district is. A perfectly compact district would be a circle, but it is impossible to fill a map with only circular districts. That said, districts should avoid sprouting ‘arms’ and the distance to the center of a district should be similar all along the boundaries (exceptions to compactness are often made for Section Two districts or to keep communities intact). For more information on multiple standard measures of compactness (e.g. Polsby-Popper, Reock, Convex Hull etc.), visit: https://redistricting.lls.edu/redistricting-101/where-are-the-lines-drawn/#compactness
- Keep as Many Communities of Interest (COIs) Intact as Possible — A community of interest is often defined as a group of people who have common policy concerns and would benefit from being maintained in a single district. Examples of this might be a neighborhood in a city, a HOA, a school district, or a Native American reservation. Redistricting often allows for public input for citizens to define their own communities of interest.
Other criteria that are sometimes used to diminish the effects of gerrymandering or are adopted for other considerations:
- Document All Iterative Changes to a Map and Summarize the Reasons Why — This criteria is sometimes put onto map drawers to show that they are adhering to the defined criteria and so that the public can see the versions and iterations the map went through. This is done to increase the transparency of the process.
- Draw Maps Blind to Incumbent Addresses — To make sure that no one is creating maps to advantage or disadvantage certain incumbents, the map drawers can be kept blind to the addresses of the incumbent representatives. This hopefully results in map drawers creating the best maps they can without taking political considerations into account.
- Draw Maps to Purposefully Avoid Grouping Incumbents into a New District — This criteria is the opposite of the above. It is sometimes used when one political party will have control over the map drawing process and use it to try to squeeze out members of the opposing party. There have been cases where partisan map drawers have purposefully grouped incumbents of the same party into one district so that only one can win, or they group incumbents of one party with a stronger incumbent of the other party to ensure they are not re-elected. Making sure incumbents are not grouped together can eliminate this, but this criteria has also been used to protect incumbents from political challenge and to keep the detrimental effects of previous maps intact.
- Multi-Member Districts- While federal law prohibits multi-member districts for Congress, many state legislatures elect several representatives from a single district.
- Nesting Requirement – In states where districts are “nested,” each lower house (e.g. state house) district is a subdivision of a larger upper house (e.g. state senate) district.
- Floterial District- Sometimes, individual districts may have a surplus population that is not significant enough to gain additional representation but still causes issues with deviation. A floterial district combines and overlaps several of these districts to meet the population requirement and add an extra representative for the combined population.
- Draw Maps without Access to Political Data — While VRA evaluation requires political data, often, redistricting criteria requires map drawers to draw the remaining districts without having election results or voter registration loaded as a layer. This prevents map drawers from trying to create partisan favoring districts.
- Draw to Create as Many Politically Competitive Districts as Possible — This is almost the opposite of the criteria above. In this version the map drawer is directed to draw as many districts as possible where results of historic statewide elections in the newly created districts are as close to 50/50 as possible.
- Draw without Considering Past Districts (aside from VRA districts) — Oftentimes, old districts were drawn for political purposes and map drawers are directed to start from scratch.
- Draw to Keep the Core of Past Districts Intact — This is the opposite of the criteria above. One of the easiest and perhaps quickest ways to draw a map is to simply update old districts to reflect population changes. However, adopting this criteria risks locking in any detrimental effects of old plans.
- Preserve as Many Voting Precincts As Possible — Oftentimes, precinct maps will be redrawn on different timelines. It is inconvenient for precincts to be split by one or more districts and have to offer different types of ballots depending which part of the precinct voters live in. For this reason redistricting consultants often try to keep voting precincts intact within a district.
- Redistributing Prisoners to their Home Addresses — If there is one or more large prisons in a jurisdiction, sometimes that prison can throw off either the average number of voters in a district (in most states, prisoners cannot vote) or distort VRA calculations. Some states or jurisdictions will attempt to assign prisoners back to their last known address for redistricting purposes. This is a good practice, but it is a relatively heavy data lift and one better adopted at the state level than done individually by a county or city. If a state does prisoner allocation, they generally release a modified PL 94-171 file with the prisoner reallocation already done. Map Drawers can incorporate this file into their drawing software to then account for this provision. For more information on states that reallocate prisoners to their home addresses, visit: https://redistrictingdatahub.org/data/ongoing-data-projects/states-that-adjust-the-census-data-for-redistricting/.
- Redistributing College Students to their Home Addresses — Similar to the above. Again, this one is generally better if it is done at the state level.
- Draw During Public or Recorded Meetings — It is possible to draw the maps during public meetings so that the public can see the process and, in some cases, provide community feedback. This is done to increase transparency and build trust in the system but requires multiple and/or longer public meetings.
- Proportionality – The proportion of voters in a jurisdiction/district who favor each political party should be similar to the voter preferences in historical elections. For example, if the population of a jurisdiction/district allotted 10 seats is 60% democratic and 40% republican, the jurisdiction/district would ideally elect 6 Democrats and 4 Republicans as representatives. This criterion is most common in multi-member districts.
Understanding and adhering to such a myriad of criteria can be a difficult task, but HaystaqDNA can help you draw fair and compliant districts. For more information on Haystaq’s services call us at 202-548-2562 or visit our contact page – https://haystaqdna.com/contact/
Common Redistricting Terms
At-Large Districts
Populations in at-large districts are not divided into several districts and the entire region votes as a cohesive unit. For example, states that are assigned one member in the House hold at-large elections across the entire state.
Reapportionment
The Permanent Apportionment Act of 1929 set the number of seats in the U.S. House of Representatives to 435. After each decennial Census, seats are redistributed to ensure proportional representation in Congress for all states.
P.L. 94-171 Redistricting Data
Public Law (P.L.) 94-171 requires the Census Bureau to provide detailed demographic data needed for redistricting. At the most granular level, the data summarizes the demographic makeup (race/ethnicity, age, etc.) of each Census Block.
Voting Age Population (VAP)
Total population of individuals who are at least 18 years old.
Citizen Voting Age Population (CVAP)
Total population of individuals that are of voting age and a U.S. citizen. This data is usually derived from the American Community Survey (ACS) data set.
Ideal Population
The ideal population size for each district is found by dividing the total population of a region by the number of districts in the respective representative body. Ideal Population = Total Population/ # of Districts
Raw Deviation
The numerical difference of a district’s population from the ideal population. Raw Deviation = District Population – Ideal Population
Percent of Deviation
The proportional difference of a district’s population from the ideal population expressed as a percentage. % of Deviation= Raw Deviation/ Ideal Population
Deviation Range
Total deviation across all districts. Found by dividing the deviation percent of each individual district and adding the absolute values of the minimum and maximum deviations. Deviation Range=abs(min(% of Deviation)) + abs(max(% of Deviation))
Cracking
Splitting communities into various districts to dilute said group’s voting power.
Packing
The opposite of cracking; concentrating certain populations into a limited number of districts to restrict the amount of representatives they can elect.
Voting Rights Act (VRA)
Passed in 1965, the Federal VRA protects voters belonging to minority and or protected groups from discrimination.
Majority-Minority District
Electoral districts in which the majority of constituents (50% or more of the citizen voting-age population) belong to racial or ethnic minorities. Where possible, creating/preserving such a district would be required by the VRA to ensure these groups can elect their candidates of choice.
Coalition District
Districts in which individual minority groups do not form a majority but vote together with other minority groups to form a coalition vote bloc in which the sum of these groups forms the majority and is able to elect a candidate of choice. Such a district, however, is not legally required by the VRA.
Opportunity District
A district where a minority group is able to elect their candidate of choice because the majority group votes similarly to them. This is also not legally required by the VRA.
Community of Interest (COI)
A community of interest COI is a group of people with shared concerns, interests, and characteristics. Every COI is unique; they might be formed around neighborhoods or the physical landscape, cultures, values, and many other things. Because of these shared interests and concerns, a common redistricting criteria is that COIs be considered during the process.
Incumbent
The current holder of an office or position.
Incumbency Criteria
Requires the incumbent’s house to remain in the district they represent.