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What Criteria Are Used to Draw District Lines?

All congressional, state legislative, and local district lines must comply with certain federal constitutional and statutory requirements, including provisions designed to ensure that districts represent an equal population and do not racially discriminate.State law governs the remaining requirements. While criteria vary from state to state, common criteria traditionally include the following.


There must be, “a minimum distance between all parts,” of the district. The boundaries of a “compact” district are generally more normal-looking and lack the contorted boundaries of the quintessential gerrymandered districts. Reasonable compactness is required for legislative districts in 32 states and congressional districts in 17 states.There are three main types of compactness.

Contorted Boundaries

Contorted boundaries, the most important measure of compactness, are the imaginative lines that encompass a district. A district with smoother, more uniform boundaries will be more compact as opposed to one with “squiggly,” or meandering, boundaries.

Dispersion Boundaries

Dispersion boundaries, the second measure of compactness, describes the degree to which the district spreads from a central core. A district that is less dispersed from its central core will be more compact while a district encompassing regions located far from its center will be less compact.

Housing Patterns

The final category of compactness refers to the relationship between housing patterns and the district’s boundaries. Under this measure of compactness, a densely populated district must have a more “normal” shape; likewise, offshoots are less worrisome for districts with a more spread out population.


Contiguity requires all areas of the district to connect at some point with the rest of the district. A district is contiguous if you can travel from any point in the district to any other point in the district without crossing the district’s boundary. In cases where districts are divided by water, they are contiguous if a common means of transport, like a bridge, connects the two sides. Contiguity is required for at least one chamber’s state legislative district in 45 states and for congressional districts in 18 states.

Preservation of Counties and Other Political Subdivisions

Districts must not cross county, city, or town boundaries. Sometimes, counties or cities must be split in order to comply with other redistricting requirements. However, many state laws do not specify, “whether it is better to minimize the number of jurisdictions that are split, or to minimize the number of times that a given jurisdiction is split.” The preservation of counties and political subdivisions is required in the drawing of state legislative districts in 34 states and in the drawing of congressional districts in 15 states.

Preservation of Communities of Interest

Communities of interest are defined as, “geographical areas, such as neighborhoods of a city or regions of a state, where the residents have common political interests that do not necessarily coincide with the boundaries of a political subdivision, such as a city or county.” Common political interests may include cultural, racial, ethnic, social, and economic interests that are probable subjects of legislation. “By constitution or statute, 15 states consider keeping ‘communities of interest’ whole when drawing state legislative districts; 11 state do the same for congressional districts.”

Preservation of Cores of Prior Districts

The preservation of the cores of prior districts refers to the maintenance of districts, to the extent possible, as previously drawn to ensure a continuity of representation. The goal is to ensure that redistricting does not introduce unnecessary racial changes to map schemes.

Avoiding Pairing Incumbents

This requirement aims to ensure that districts avoid creating contests between incumbents. This is done primarily in the interest of the district party’s long-standing goal. By contrast, some states have recently adopted criteria that prohibit map drawers from favoring an incumbent, candidate, or political party.

Partisan Competitiveness

Some states have recently adopted a requirement that districts have a fairly even number of residents from the major political parties in to make elections more competitive.

What Are the Legal Requirements?

Regardless of who is drawing the lines, all line drawers must comply with the districting rules created by the United States Constitution and federal law. Each state generally has their own rules when it comes to what a line drawer may or may not consider when drawing maps.

Federal Rules 

There are two major requirements for line drawing under the U.S. Constitution—equal population and the prohibition on racial discrimination.

Equal Population

Often called the doctrine of One Person, One Vote, the United States Supreme Court has found that congressional, state, and local legislative districts must generally be of equal population.

Congressional Districts

Congressional districts must be as equal as practicable. This requirement comes, in part, from the Supreme Court’s decision in Wesberry v. Sanders, where the Court held that, “the command of Art. I, s 2, that the Representatives be chosen ‘by the People of the several States’ means that as nearly as is practicable one man’s vote in a congressional election is to be worth as much as another’s.”

Later cases on congressional apportionment have found that congressional districts are permitted to have some deviations from complete equality in population, but these deviations must be small and justified by a legitimate state policy. Despite permitting some deviation in earlier challenges to congressional maps, in Evenwel v. Abbott, the Supreme Court again reiterated that, “States must draw congressional districts with populations as close to perfect equality as possible.”

As such, the guiding standard for congressional districts is, “close to perfect equality as possible.”

State and Local Legislative Districts

Historically, in Reynold v. Sims, the Court found that the one person, one vote doctrine applied to state apportionment schemes, meaning that state legislative districts required equal population.  The Reynolds Court wrote that:

By holding that as a federal constitutional requisite both houses of a state legislature must be apportioned on a population basis, we mean that the Equal Protection Clause [of the Fourteenth Amendment] requires that a State make an honest and good faith effort to construct districts, in both houses of its legislature, as nearly of equal population as is practicable.

In Avery v. Midland County, the Court applied the one person, one vote principle to local election districts, finding that voters in local jurisdictions were constitutionally entitled to having their votes carrying a substantially similar weight to that of any other voter.

As of 2021, One Person, One Vote applies to congressional, state legislative, and local election districts. The Supreme Court has, however, upheld population deviations for state legislative and local apportionment that achieve only substantial population equality. In the context of state and local legislative districting, districts may deviate from perfect population equality, “[w]here the maximum population deviation between the largest and smallest district is less than 10%[. A] state or local legislative map presumptively complies with the one-person, one-vote rule,” as long as the deviations are justified by a “legitimate consideration.”

Despite having larger permissible deviations, any deviation from absolute equality, no matter how small, still must be justified by “legitimate considerations.”

Population Basis

Currently, nearly every jurisdiction utilizes total population to equalize districts. Under the U.S. Constitution, total population has been found to be the only permissible population basis for congressional districts. In Evenwel v. Abbott, the Court held that state and local election districts, “may draw its legislative districts based on total population.” The question of whether a state could use citizen voting age population to redistrict, if permitted under state law, is not yet resolved but there are good arguments that such a system would run afoul of federal law.

Drawing Lines Based on Race

Under the United States Constitution, it is impermissible to use race as the predominant factor in deciding how to draw congressional, state, and local legislative districts. There are exceptions to this rule, such as drawing the lines to ensure that a district is not causing harm to minority voters. Moreover, under the Constitution and the Federal Voting Rights Act (VRA) map drawers are prohibited from drawing districts with the intent to diminish the voting power of communities of color. Under the VRA alone, maps with the effect of diminishing the voting power of communities of color are similarly forbidden.

While this scheme may seem confusing, the main rules are enumerated below in numerals. Accompanying each rule is an example of how it is applied or manifests.

1. No Intentional Racial Discrimination

Line drawers cannot draw district lines with the purpose of harming voters of a protected class.

In Gomillion v. Lightfoot, a local act altered a city’s boundary lines from a square to a 28-sided figure. The new city shape virtually removed all Black voters from the city, leaving only 4 or 5 Black voters in the new shape, while not removing any white voters or residents. The Supreme Court determined that the new shape and the removal of almost all Black residents was crafted for the purpose of removing Black voters from the electorate and therefore violated the Fifteenth Amendment of the Constitution. This reasoning has since been extended to the Fourteenth Amendment.

2. Governments Must Have Compelling Reason for Racial Consideration

Race can be considered when drawing district if the government has a compelling reason for doing so, but it cannot be the only consideration when drawing a district. Simply put, race cannot be the “predominate” factor.

In Cooper v. Harris, the North Carolina legislature had instructed line drawers to increase or pack the Black population into a congressional district that had already consistently elected the Black community’s candidate of choice. The result of increasing the Black population in this district was to decrease the Black voting power in neighboring districts. While the Court acknowledged that race can be considered where necessary to further a compelling interest, such as compliance with Section 2 of the Voting Rights Act, in this case, the use of race was not necessary. Because Black voters in the district already consistently elected their candidate of choice with the support of some white voters, Section 2 of the VRA did not require the legislature to draw a new majority-minority district. The Court thus found that “the use of race as the predominate factor in designing [the] district ” was unconstitutional.

3. Election Schemes Cannot Limit A Minority Group’s Ability to Elect Candidates of Choice

If an election scheme, including the use of a district map, has the effect of limiting the ability for a protected class (minority voters) to elect a candidate of their choice, then the district scheme may violate the Voting Rights Act.

Map drawers likely violate Section 2 of the Voting Rights Act if they fail to draw a majority-minority district where there is present or historic discrimination in the state or locality. Majority-minority districts may be drawn when, along with appropriate historical evidence: (1) there is a large enough community of color in a state or locality to make up 51% of the voting population in a reasonably compact district; (2) voters of color and white voters consistently vote for different candidates; and (3) white voters consistently prevent voters of color from electing their candidate of choice.

In League of United Latin Am. Citizens v. Perry, 548 U.S. 399 (2006), the Texas Legislature enacted a new redistricting plan in 2003. Voting rights advocates challenged the maps and, in part, brought a cause of action under Section 2 of the Voting Rights Act, alleging that Texas’s congressional District 23 diluted Latino voters’ ability to elect a candidate of choice because it broke apart the growing Latino community in that part of Texas between multiple districts. The Supreme Court found that the plan violated Section 2 of the Voting Rights Act based on the fact that the growing Latino population in District 23 had experienced historical discrimination in voting and that the State’s districting plan “took away the Latinos’ opportunity because Latinos were about to exercise” their ability to elect candidate of their choice in District 23.

State Legal Requirements 

All 50 states have their own state-level legal requirements for redistricting in addition to the federal requirements. Further, states may have different requirements for the redistricting of congressional districts and state or local election districts.

Traditional Requirements

Many state constitutions or statutes set forth requirements that map drawers must comply with when drawing district lines. Common state legal requirements include: geographically compact districts; contiguity; preserving pre-existing counties, cities, and towns; and preserving communities of common interest.

State Law Protections

A majority of states have affirmative protections for elections enshrined in their state constitutions. In general, these clauses require elections to be free, fair, or equal, or protect a voter’s right against improper election or voting manipulation by civil or military powers.

Some states also have their own versions of the Voting Rights Act. In California, for example, places that vote using an at-large method of election, where all voters vote on all candidates instead of voters voting in specific districts, can challenge this method of election if it weakens a minority group’s ability to elect a candidate of its choice. Washington State follows a similar model, codified in the Washington Voting Rights Act.

If your state does not yet enshrine voter protections in state law, check out UCLA VRP’s Model State Voting Rights Act as a guide.

State Protections Against Partisan Gerrymandering

Although partisan gerrymanders cannot currently be challenged in federal courts,voters have had significant success challenging partisan congressional and state legislative maps in state courts under their state’s constitution.

Generally, these challenges are brought under a state’s Free and Equal Elections Clause, sometimes called a Free and Fair Elections Clause, and the state constitutional analogs of the First and Fourteenth Amendments of the U.S. Constitution. Under these clauses, states voters, residents, and grassroots organizations have been able to challenge district maps that dilute the vote of a specific party. In one case, the court struck down the gerrymandered maps because, “the carefully crafted maps, and not the will of the voters . . . dictate[d] the election outcomes in a significant number of legislative districts and, ultimately, the majority control” of the legislature.

Successful cases include:

  • Common Cause v. Lewis, No. 18 CVS 014001, 2019 WL 4569584 (N.C.Super. Sep. 03, 2019), which struck North Carolina’s state legislative districts as a partisan gerrymander;
  • Harper v. Lewis, No. 19 CVS 012667, which struck North Carolina’s congressional district maps as an impermissible partisan gerrymander; and
  • League of Women Voters v. Commonwealth, 645 Pa. 1, 178 A.3d 737 (2018), which successfully challenged Pennsylvania’s congressional map as an impermissible partisan gerrymander in violation of the state constitution.