The U.S. Constitution requires that legislative and congressional districts get redrawn at least once every 10 years using new census data to guarantee equal representation, and the states are in charge. With the 2020 census fast approaching, preparations are beginning in earnest.
Three years prior to the census (and four years prior to drawing new maps), legislatures are looking at the criteria, or principles, that guide the work. Legislative committees have adopted criteria in previous cycles to help manage what can be a difficult process. Agreed-upon criteria also help legislatures comply with very complex legal requirements and ensure fairness and consistency. Some criteria are applicable to all states; others are state-specific.
Universally Applicable Criteria
The universally applicable criteria stem from the U.S. Constitution and federal law. Perhaps the most important of these is “one person, one vote,” which means all people in the United States must be equally represented in legislative bodies; i.e., legislators in the same body must represent roughly the same number of people.
The one-person, one-vote standard is different for congressional districts than for state and local districts. Congressional districts must be as equal as is “practicable” in terms of population, whereas state legislative districts must be “substantially equal.” State legislative districts can have some population deviation, but only if there is a compelling state rea- son to do so, such as adhering to other established criteria.
The other universal criterion that applies to all redistricting is compliance with the Voting Rights Act and the Equal Protection clause of the 14th Amendment, which prohibit states from drawing district lines in a way that dilutes the voting power of minority groups. At the same time, the Supreme Court has ruled that race cannot be the predominant factor in drawing district lines.
Besides the universal principles, legislative map- makers often have additional criteria to meet, as established in the constitution, by statute or as adopted by chambers or committees. Courts have identified six “traditional districting principles” that are common to many states. These include two that are based on geography:
- Compactness (a measure of a district’s geometric shape)
- Contiguity (all parts of the district must be connected)
The other traditional districting principles are:
- Adhering to pre-existing political subdivisions (such as city and county lines)
- Preserving communities of interest (such as neighborhoods or regions where the residents have common political interests)
- Preserving the cores of prior districts (to provide continuity of representation)
- Protecting incumbents (by avoiding contests between incumbents that could result if a new district included residences of two or more sitting representatives).
Newer Redistricting Criteria
States can choose to adopt criteria outside the tradi- tional districting principles as well. In recent years, some states and legislatures have adopted criteria trying to limit partisan gerrymandering.
Redistricting Criteria for Legislative Maps
- Prohibiting political data. An increasing number of states prohibit the use of political data, such as party affiliation or voter history in their redistricting datasets. Iowa is the best example of a state using this criterion.
- Not drawing districts to favor or disfavor political parties or incumbents. This focuses on the intent behind how lines are drawn. This criterion does not prohibit the use of political data, but such data may not be used with the intention of favoring or disfavoring a political party or incumbent. Florida’s constitution includes this language.
- Encouraging competitiveness. Some states, such as Arizona, require that district lines be drawn in a way that increases interparty competitiveness: “to the extent practicable, competitive districts should be favored where to do so would create no significant detriment to the other goals.” By requiring competitiveness, advocates hope to prevent the creation of too many “safe districts,” or districts that lack interparty competition due to a party’s dominance among the electorate. Critics of this approach claim that drawing districts with a goal of competitiveness leads to maps that violate compactness and other traditional criteria.
Criteria, whether traditional or otherwise, can conflict. No matter who draws the maps—legislators or a commission—balancing a list of criteria may require prioritization. California, for instance, explicitly ranks its criteria in the state constitution.
Finally, other criteria might define the timetable for completing maps, how much deviation in population will be accepted or what data will be used for redistricting. For example, a handful of states adjust the census data before starting the process to exclude college students or to reallocate incarcerated people to a home address.
Legislation relating to state-specific redistricting cri- teria is common. Many of these bills propose prohibitions on the use of political data or adopting concepts such as competitiveness.
Other bills relate to defining exactly what is meant by a given criterion. When a definition isn’t explicit, the task of interpreting the law is left to the courts. In the case of compactness, Colorado (Colo. Const. art. V, § 47) defines it as making the “aggregate linear distance” of district lines as short as possible.
In the case of “communities of interest,” very few states define the phrase. Alaska (Alaska Const. art. VI, § 6) was one of the first states to give the term a specific meaning. According to its constitution, all Alaskan districts must include a relatively integrated socio-economic area.
While redistricting is a state function, the Supreme Court plays an outsized role in the process, taking on redistricting cases frequently—almost every session. Many cases are based on interpretation of these criteria.
In a case slated for this fall, the Supreme Court will address a potentially groundbreaking theory that seeks to define partisanship—how much partisanship tilt is too much to pass constitutional muster? In late 2016, a federal district court found in Whitford v. Gill that the Wisconsin General Assembly in 2012 adopted legislative district maps that favored Republicans so much that they violated the First and Fourteenth Amendments to the U.S. Constitution. If the Supreme Court affirms the trial court’s finding, it will set for the first time a legal standard to limit partisan map drawing.