Redistricting is how the United States redraws the boundaries of its congressional, state legislative, and local election districts after each census so that each district holds roughly the same number of people. Understanding how redistricting works means following a chain that runs from the census count, to the body that draws the lines in each state, to the federal and state rules those lines have to satisfy, to the moment a final map is adopted or imposed by a court.
The Census Kicks Off Every Cycle
Article I, Section 2 of the U.S. Constitution directs Congress to conduct an “actual Enumeration” of the population every ten years.1Congress.gov. U.S. Constitution Article I – Section: Section 2 That count includes everyone living in the country, citizens and noncitizens alike, and its results drive the entire redistricting process from Congress down to local school boards.
After the count, the federal government reallocates the 435 U.S. House seats among the 50 states. States that grew faster than the national average may gain seats; slower-growing states may lose them. But apportionment alone doesn’t produce district lines. For that, states need finer data.
Public Law 94-171, passed in 1975, requires the Census Bureau to deliver population tabulations to the states within one year of census day, broken down for the small geographic areas each state has identified for redistricting.2U.S. Government Publishing Office. Public Law 94-171 – Population Tabulation for State Legislative Apportionment The Bureau publishes the data down to the census block, its smallest unit of geography, and the files include tables on race, Hispanic or Latino origin, and voting-age population. Those categories matter because mapmakers need them to evaluate compliance with the Voting Rights Act.3U.S. Census Bureau. Decennial Census P.L. 94-171 Redistricting Data Summary Files
Who Draws the Lines
There is no national body that draws district maps. Authority belongs to each state, and the process varies with state constitutions and statutes.
In most states, the state legislature controls redistricting for both congressional and state legislative districts. Legislators propose maps, debate them, and pass them through ordinary lawmaking, usually a majority vote in both chambers plus the governor’s signature. The obvious concern is that the party in power effectively chooses its own voters, which is why this model attracts the most criticism.
Other states have shifted some or all responsibility to commissions. Structures differ widely. Some commissions are made up entirely of non-politicians and operate independently of the legislature. Some include elected officials. Others are purely advisory, recommending maps to the legislature without final authority. Composition rules vary too: some require equal representation from each major party plus unaffiliated tiebreakers, while others use applicant screening designed to filter out strong partisan ties.
Redistricting Between Censuses
Redistricting traditionally happens once per decade, but nothing in federal law prevents a state from redrawing its maps more than once between censuses. In 2025 and 2026, several states pursued mid-decade redistricting at rates not seen since the 1800s, with legal fights over those changes moving through both state and federal courts. The ten-year cycle is a strong norm, not a legal ceiling.
What Every Map Has to Satisfy
Whichever body draws the maps, every plan has to meet federal constitutional and statutory requirements. Two principles do most of the work: population equality and protection of minority voting rights.
One Person, One Vote
The Equal Protection Clause of the Fourteenth Amendment requires electoral districts to hold substantially equal populations. For congressional districts, courts demand near-exact equality, and even small percentage deviations can be struck down if they lack a legitimate justification. State legislative districts get more flexibility: deviations under ten percent from the ideal district size are generally presumed constitutional, though they can still be challenged if the evidence suggests the deviation was designed to favor one group.
The Voting Rights Act
Section 2 of the Voting Rights Act of 1965, codified at 52 U.S.C. ยง 10301, prohibits any voting practice or procedure that denies or restricts the right to vote based on race, color, or membership in a language minority group. For redistricting, that means mapmakers cannot draw lines that dilute the voting strength of minority communities, whether intentionally or as a practical consequence of the map’s design.4United States Department of Justice. Redistricting Information – Section: Section 2 of the Voting Rights Act
Courts evaluating Section 2 claims ask whether the challenged map gives minority voters an equal opportunity to participate and elect candidates of their choice. In Thornburg v. Gingles (1986), the Supreme Court set three preconditions a minority group must show before a Section 2 violation can be found: the group must be large and geographically compact enough to form a majority in a single district, it must be politically cohesive, and the white majority must vote as a bloc frequently enough to usually defeat the minority group’s preferred candidates. Only if all three are met does the court then examine the totality of the circumstances.
The Act originally included a preclearance requirement under Section 5, which forced certain jurisdictions with histories of discrimination to obtain federal approval before changing voting procedures, including redistricting plans. The Supreme Court effectively disabled that requirement in 2013 by striking down the coverage formula. Section 2, which applies nationwide and requires no preclearance, now carries the primary enforcement burden for redistricting challenges under the Act.5United States Department of Justice. Redistricting Information
Traditional Principles That Shape District Shapes
Beyond the hard legal requirements, mapmakers in most states follow a set of traditional principles. These aren’t federally mandated, but many states have written them into their own constitutions or statutes, and courts consider them when evaluating whether a map was drawn in good faith.
- Compactness. Districts should have a reasonably regular shape rather than stretching across long distances or snaking through narrow corridors.
- Contiguity. Every part of a district must be physically connected so a person could travel from one end to the other without leaving it. Most states make exceptions for areas separated by water.
- Preserving political subdivisions. Mapmakers try to avoid splitting counties, cities, and towns when population numbers allow.
- Communities of interest. Groups that share social, economic, or cultural ties are kept together when possible, whether that’s a manufacturing corridor, a tribal community, or a university town.
These principles matter in litigation. A map that respects traditional criteria looks like it was drawn for legitimate reasons. A map that flagrantly violates compactness or fractures communities without explanation often signals to a court that something else was driving the pen.
Gerrymandering
Gerrymandering is the deliberate manipulation of district boundaries to benefit a particular party, group, or incumbent. The term dates to 1812, and the two core techniques appear in nearly every dispute:
- Packing. Concentrating opposing voters into as few districts as possible, giving them overwhelming margins in those districts but wasting their votes elsewhere.
- Cracking. Splitting opposing voters across multiple districts so they never form a majority in any of them.
Both techniques can produce maps where one party wins far more seats than its statewide vote share would suggest. A party with 55 percent of voters statewide can, through careful line-drawing, win 70 or 80 percent of the seats.
Racial Gerrymandering
Racial gerrymandering occurs when race is the predominant factor in drawing district lines without a compelling justification. The Supreme Court has held that sorting voters primarily by race violates the Equal Protection Clause, even when the stated purpose is to help minority communities. The key question is whether race was the dominant motivation overriding traditional districting principles. If it was, the map must survive strict scrutiny: the state has to show the racial sorting was narrowly tailored to serve a compelling government interest, such as compliance with the Voting Rights Act.
Partisan Gerrymandering
Partisan gerrymandering has been much harder to police in federal court. In Rucho v. Common Cause (2019), the Supreme Court held that claims of excessive partisan gerrymandering are “political questions beyond the reach of the federal courts.” The majority concluded that while partisan gerrymandering may be “incompatible with democratic principles,” the Constitution does not give federal courts manageable standards for deciding when partisanship in redistricting crosses a constitutional line.6Supreme Court of the United States. Rucho v. Common Cause, 588 U.S. 684 (2019)
The opinion did not endorse partisan gerrymandering. It explicitly noted that “provisions in state statutes and state constitutions can provide standards and guidance for state courts to apply.”6Supreme Court of the United States. Rucho v. Common Cause, 588 U.S. 684 (2019) Roughly 30 state constitutions contain some form of “free elections” clause, and 18 of those further require elections to be “equal” or “open.” Several state supreme courts have used these provisions to strike down maps as excessively partisan. Pennsylvania threw out a congressional map in 2018 under its “free and equal elections” clause. State courts, applying state constitutions, are now the main forum for partisan gerrymandering challenges.
How Prisoners Get Counted
A subtler distortion comes from how incarcerated people are counted. The census counts prisoners at the facility where they are housed, not at their home address. Because prisons often sit in rural areas far from the urban communities where most prisoners lived before incarceration, the practice inflates the population of rural districts and deflates the count in the communities that lose those residents. Non-incarcerated residents of a prison district end up with outsized political influence.
As of early 2026, nineteen states have enacted some form of legislation to address this. Some count incarcerated people at their last known home address for redistricting purposes. Others allocate prisoners with unknown or out-of-state addresses into a statewide pool rather than assigning them to the prison’s district. At least one state excludes prisoners from a district’s population total entirely. Most states, however, still count prisoners where they are incarcerated.
Public Input and Final Adoption
Most redistricting processes include some opportunity for public participation. At least 26 states have formal provisions in their constitutions or statutes governing public involvement. In practice, that usually means public hearings where residents can review proposed maps and testify about how boundary changes would affect their communities. Some states accept written comments or let residents submit their own proposed maps using publicly available software.
The mechanism for final adoption depends on who drew the map. In legislature-controlled states, it passes through both chambers as a bill and goes to the governor for signature or veto. In commission-led states, the commission votes to certify the final map and files it with the secretary of state or an equivalent office. Once adopted, the new boundaries are loaded into voter registration systems and take effect for the next election cycle.
When the process breaks down and no map is adopted in time for upcoming elections, courts step in. Judges may appoint a special master to draw the lines, or they may order the state to use a previously submitted map with modifications. Court-drawn maps tend to adhere closely to traditional districting principles and avoid the more aggressive partisan choices that legislative maps sometimes reflect. The prospect of losing control to a court often pushes deadlocked bodies to compromise, though in recent cycles several states have ended up with judicially imposed maps anyway.