Census – The survey of the U.S. population that occurs at in the first year of every decade. The U.S. Constitution charges Congress with counting every person in the census enumeration, including citizens, children, and undocumented persons. Data from the census is used to determine the number of congressional seats each state receives and it has been used traditionally to ensure that districts have equal population and comply with other legal requirements such as the Voting Rights Acts. The Census Bureau is the government agency that administers the census. The next census is in 2020.
Commission – A constitutional or statutory authority that some states use to draw district boundaries after a census. For purposes of this guide, we group commissions into four categories:
Advisory commission – A commission that draws a map for consideration by another body such as a legislature. Unlike other commissions, an advisory commission does not have the legal power to pass a binding map. The membership of an advisory commission may consist of legislators, non-legislators, or a mix. Five states currently use an advisory commission for legislative plans and three states currently use an advisory commission for congressional plans.
Backup commission – A commission that draws plans only if the legislature cannot agree on a map or when the governor vetoes a proposal and no new map is passed. Five states currently use a backup commission for legislative plans and two states use a backup commission for congressional plans. The composition of backup commission varies by states. In Texas and Mississippi for example, the backup commission is made up of specific statewide officials. In Maryland, the governor’s proposal becomes the default plan if the legislature fails to approve a map. Members of the legislature form the backup commission in Connecticut, Illinois, and Oklahoma.
Independent commission – A commission composed of individuals who are neither legislators or other public officials and who are selected after a screening process conducted by an independent entity. Legislators may not serve on the commission. Two states currently use an independent commission for both legislative plans and congressional plans.
Political appointee commission – A commission composed, in whole or in part, of individuals who are directly appointed by elected officials or party leadership. In some states, the membership of a political appointee commission is evenly divided between parties but, in other states, there could be more members of one party than the other. Nine states currently use a political appointee commission for legislative plans and four states currently use a political appointee commission for congressional plans.
Politician commission – A commission composed entirely of lawmakers or other elected officials. Politician commissions usually are appointed by the legislative or party leadership, the governor, or chief justice of the state supreme court, two states currently use a politician commission for legislative plans and no state currently uses one for congressional plans.
Deviation – The percentage by which a district’s population can vary from perfect parity where all districts have the exact same population. The Supreme Court has interpreted the Constitution as requiring that congressional districts have a deviation of no more than one or two persons from population parity. However, the Court has given states more flexibility when drawing legislative boundaries, in general permitting districts to deviate by up to 10 percent between the largest and smallest districts. Some states impose rules that further limit permitted deviations.
Equal population – A constitutional requirement that each congressional district should have more or less the same number of people with next to no population deviation. State legislative districts also are constitutionally required to have equal population, but courts have permitted state legislative districts somewhat greater population deviations. A state must have a good reason, supported by state policy, to justify a district with more or less people than the ideal population.
Reapportionment – Reapportionment has two meanings. First, it refers to the constitutionally required act of redistributing seats in Congress based on each state’s proportion of the nation’s population following a census. Secondly, some states, use reapportionment as a synonym for redistricting.
Redistricting – The act of redrawing lines for electoral districts every ten years after a census in order to ensure that districts have equal population and comply with other legal requirements. States redistrict congressional and legislative boundaries, and many local governments, such as cities, counties, and school boards also redraw district boundaries every ten years. Redistricting is sometimes referred to as reapportionment.
State-Level Criteria – The legal requirements which a state must follow when drawing district lines. In some instances, states will list these conditions in a ranked order, requiring high-priority criteria to be satisfied before other standards. Most states, however, list these principles without a ranked order of priority. Some states include instructions to follow specific guidelines “where practicable,” signaling that specific criteria should be considered only when feasible amongst the other criteria. Below are a few examples of common criteria:
Be Compact – Many states require that districts be compact. But few states actually define exactly what compactness means. Exceptions are states like Iowa that define compactness by particular statistical measures.
Be Contiguous – States commonly impose a requirement of contiguity. Contiguity means that the boundaries of a district are a single, uninterrupted shape; a person should be able to travel across a district without crossing into another district. Some states have specific provisions for special circumstances such as for districting around water and islands.
Preserve Communities of Interest – A few states require districting plans to make an effort to preserve communities of interest. A community of interest refers to group of people who are likely to have common legislative concerns and might benefit from collective representation in the legislature. Communities of interest may be defined by racial and ethnic demographics, economic opportunities, and or geographic region. Other criteria such as following county, city, and town boundaries could be proxies for recognizing communities of interest. Relationships with a political party, incumbent, or candidate are sometimes excluded from this definition.
Follow Natural Boundaries – Some states require district boundaries to adhere to naturally occurring barriers, such as bodies of water or a mountain range.
Follow Political Boundaries – States commonly require that districts minimize the splitting of counties, cities, towns or wards. Similar to contiguity, states may provide specific guidelines for how to split these boundaries if necessary to achieve other goals.
Nest Senate and House Districts – A few states require the geographic boundaries of two or more house districts to be contained within senate districts. Nesting can be accomplished by drawing house districts, and consolidating the boundaries to form senate districts, or by establishing senate districts first and dividing those boundaries into house districts.