Redistricting and Gerrymandering
Every ten years, following the decennial census, the United States redraws the lines of its congressional and state legislative districts. This process — redistricting — is one of the most consequential and politically charged activities in American democracy. The way district lines are drawn determines which voters are grouped together, which candidates can win, and which party controls legislative bodies. When district lines are manipulated to favor a particular party or group, the practice is called gerrymandering — a term dating to 1812, when Massachusetts Governor Elbridge Gerry signed a redistricting plan that included a district so contorted it resembled a salamander. This page examines the census, the reapportionment process, how redistricting works in practice, the legal framework governing gerrymandering, and the reform efforts aimed at making the process fairer.
The Census and Reapportionment
Article I, Section 2 of the Constitution requires an "actual Enumeration" of the population every ten years for the purpose of apportioning seats in the House of Representatives among the states. The Census Bureau, a component of the Department of Commerce, conducts this count. The census is a massive logistical undertaking, requiring the enumeration of every person residing in the United States — citizens and noncitizens alike — regardless of their legal status. The Fourteenth Amendment specifies that apportionment is based on "the whole number of persons in each State," not the number of citizens or eligible voters.
After the census results are tabulated, the Census Bureau provides the President with the apportionment population for each state. The President transmits this information to Congress, and the 435 seats in the House of Representatives are allocated among the 50 states using a mathematical formula known as the method of equal proportions (also called the Huntington-Hill method). Every state is guaranteed at least one seat. The remaining 385 seats are allocated based on population, with the method of equal proportions determining the priority order in which additional seats are assigned. 2 U.S.C. 2a.
Reapportionment can shift political power significantly. Population growth in Sun Belt states over recent decades has resulted in those states gaining seats while states in the Rust Belt and Northeast have lost them. After the 2020 census, Texas gained two seats, while Colorado, Florida, Montana, North Carolina, and Oregon each gained one. California, Illinois, Michigan, New York, Ohio, Pennsylvania, and West Virginia each lost one seat. These shifts alter the Electoral College map as well, since each state's electoral votes equal its total congressional delegation (House seats plus two senators).
The census itself has become politically contested. The Trump administration's attempt to add a citizenship question to the 2020 census was blocked by the Supreme Court in Department of Commerce v. New York, 588 U.S. 752 (2019), which held that the stated rationale for adding the question — enforcement of the Voting Rights Act — was pretextual. Critics of the citizenship question argued that it would depress response rates among immigrant communities, producing an undercount that would shift political representation away from states with large immigrant populations. The accuracy and completeness of the census count directly affect the fairness of reapportionment and redistricting, making census methodology a matter of significant political consequence.
How Redistricting Works
Once seats are reapportioned among the states, each state that has more than one congressional seat must draw new district boundaries. The Constitution assigns the authority to regulate the "Times, Places and Manner" of federal elections to state legislatures, subject to congressional override. Article I, Section 4. In practice, this means that the redistricting process varies substantially from state to state.
In the majority of states, the state legislature draws congressional district maps, typically subject to the governor's veto. This arrangement gives the party that controls the state government at the time of redistricting an enormous advantage: it can draw district lines that maximize its own seats while minimizing the opposition's. The same legislature also draws the lines for state legislative districts, creating the potential for a self-reinforcing cycle in which the party in power draws districts that entrench its majority.
Several states have established independent or bipartisan commissions to handle redistricting, removing the process from the legislature entirely or giving a commission the first opportunity to draw maps. California's Citizens Redistricting Commission, established by voter initiative in 2008 (Proposition 11) and expanded to include congressional districts in 2010 (Proposition 20), is among the most prominent. Arizona, Colorado, Michigan, and several other states have also adopted commission-based redistricting. The Supreme Court upheld the constitutionality of independent redistricting commissions in Arizona State Legislature v. Arizona Independent Redistricting Commission, 576 U.S. 787 (2015), rejecting the argument that the Elections Clause requires redistricting to be performed by the state legislature itself.
The One Person, One Vote Principle
The foundational legal principle governing redistricting is the requirement of population equality among districts. Before the 1960s, many states had not redrawn their legislative districts in decades, resulting in enormous population disparities — urban districts might have ten or twenty times the population of rural districts, meaning that rural voters had vastly disproportionate representation. The Supreme Court intervened in a series of landmark decisions that transformed American politics.
In Baker v. Carr, 369 U.S. 186 (1962), the Supreme Court held that challenges to legislative apportionment present justiciable questions under the Equal Protection Clause — overruling the long-standing position that redistricting was a "political question" beyond judicial competence. In Reynolds v. Sims, 377 U.S. 533 (1964), the Court held that both chambers of a state legislature must be apportioned on the basis of population — the "one person, one vote" principle. Chief Justice Earl Warren later described Reynolds as the most important case decided during his tenure. In Wesberry v. Sanders, 376 U.S. 1 (1964), the Court applied the population equality requirement to congressional districts under Article I, Section 2.
The population equality requirement is applied more strictly to congressional districts than to state legislative districts. For congressional districts, the Supreme Court has required near-mathematical equality, striking down deviations as small as 0.7 percent in Karcher v. Daggett, 462 U.S. 725 (1983). For state legislative districts, the Court has permitted greater flexibility, generally allowing total population deviations of up to 10 percent without requiring justification, while deviations exceeding 10 percent create a presumption of unconstitutionality. Brown v. Thomson, 462 U.S. 835 (1983).
Racial Gerrymandering
The Voting Rights Act of 1965, 52 U.S.C. 10301 et seq., imposes additional constraints on redistricting to protect minority voting rights. Section 2 of the VRA prohibits voting practices — including redistricting plans — that result in the denial or abridgment of the right to vote on account of race, color, or membership in a language minority group. Under the framework established in Thornburg v. Gingles, 478 U.S. 30 (1986), a Section 2 vote dilution claim requires proof that a minority group is sufficiently large and geographically compact to constitute a majority in a single-member district, that the minority group is politically cohesive, and that the majority votes sufficiently as a bloc to defeat the minority group's preferred candidates.
Section 5 of the VRA required jurisdictions with a history of discriminatory voting practices to obtain "preclearance" from the Department of Justice or a federal court before implementing any change to their voting procedures, including redistricting. In Shelby County v. Holder, 570 U.S. 529 (2013), the Supreme Court invalidated the coverage formula used to determine which jurisdictions were subject to preclearance, effectively rendering Section 5 inoperable. This decision eliminated the most powerful federal tool for preventing discriminatory redistricting before it takes effect, shifting enforcement to after-the-fact litigation under Section 2.
The Supreme Court has also held that race cannot be the predominant factor in drawing district lines unless the use of race satisfies strict scrutiny — meaning it must be narrowly tailored to achieve a compelling governmental interest. Shaw v. Reno, 509 U.S. 630 (1993); Miller v. Johnson, 515 U.S. 900 (1995). Compliance with the Voting Rights Act can constitute a compelling interest justifying the use of race in redistricting, but the state must have a "strong basis in evidence" for concluding that the VRA requires the creation of a majority-minority district. Alabama Legislative Black Caucus v. Alabama, 575 U.S. 254 (2015). In Allen v. Milligan, 599 U.S. 1 (2023), the Court reaffirmed the Gingles framework and struck down Alabama's congressional map for likely violating Section 2 by failing to include a second majority-Black district.
Partisan Gerrymandering
Partisan gerrymandering — the manipulation of district lines for partisan advantage — has been practiced since the earliest days of the Republic. The two primary techniques are "packing" (concentrating the opposing party's voters into a small number of districts that the opposition wins by overwhelming margins, wasting their votes) and "cracking" (dispersing the opposing party's voters across multiple districts so they cannot form a majority in any). Modern gerrymandering has become dramatically more effective due to sophisticated mapping software, granular voter data, and computational methods that allow mapmakers to optimize partisan advantage with surgical precision.
The constitutional status of partisan gerrymandering was a persistent question for decades. In Davis v. Bandemer, 478 U.S. 109 (1986), a plurality of the Supreme Court held that partisan gerrymandering claims are justiciable but failed to agree on a workable standard for adjudicating them. For more than 30 years, courts struggled to develop a judicially manageable standard for distinguishing permissible partisan considerations in redistricting from unconstitutional partisan gerrymandering.
In Rucho v. Common Cause, 588 U.S. 684 (2019), the Supreme Court resolved this question by holding that partisan gerrymandering claims present nonjusticiable political questions that are beyond the reach of the federal courts. Chief Justice Roberts, writing for a 5-4 majority, concluded that "partisan gerrymandering claims present political questions beyond the reach of the federal courts" because there are no "judicially discoverable and manageable standards for resolving" them. The Court acknowledged that "excessive partisanship in districting leads to results that reasonably seem unjust" but concluded that the Constitution commits the regulation of partisan gerrymandering to Congress and the state governments, not to the federal judiciary.
The Rucho decision closed federal courts to partisan gerrymandering claims but left open other avenues for reform. State courts may adjudicate partisan gerrymandering claims under state constitutional provisions, and several have done so — the Pennsylvania Supreme Court struck down a congressional map as a partisan gerrymander under the state constitution in League of Women Voters of Pennsylvania v. Commonwealth (2018), and the North Carolina Supreme Court did the same in Harper v. Hall (2022), though the North Carolina court later reversed itself in 2023 after a change in the court's composition. Congress retains the authority under the Elections Clause to regulate congressional redistricting, though efforts to enact federal anti-gerrymandering legislation have not succeeded.
Independent Redistricting Commissions
The reform most widely adopted to address gerrymandering is the independent redistricting commission. These commissions vary in structure, but their common feature is the removal of redistricting authority — entirely or partially — from the state legislature. As of 2025, approximately a dozen states use independent or bipartisan commissions for congressional redistricting, state legislative redistricting, or both.
California's Citizens Redistricting Commission consists of 14 members: five registered Democrats, five registered Republicans, and four members who are not affiliated with either major party. Members are selected through an application and screening process designed to minimize legislative influence. The commission must draw districts that comply with the federal Constitution and the Voting Rights Act; achieve population equality; are geographically contiguous; keep together cities, counties, neighborhoods, and communities of interest to the extent possible; and are compact. Partisan considerations are expressly prohibited.
Michigan's Independent Citizens Redistricting Commission, established by a ballot initiative in 2018, has a similar structure: 13 members, divided among Democrats, Republicans, and independents, selected through a random process from a pool of applicants. Colorado's independent commissions — one for congressional redistricting and one for state legislative redistricting — include both appointed members and members selected by judicial officials.
The effectiveness of independent commissions in reducing partisan gerrymandering is a subject of ongoing evaluation. Studies of maps drawn by commissions generally find that they produce more competitive districts and more proportional representation than maps drawn by legislatures, though commissions are not immune to political pressures and their outcomes depend heavily on their specific structural features, including member selection processes, decisional criteria, transparency requirements, and the availability of judicial review.
Traditional Redistricting Criteria
Beyond the legal requirements of population equality and compliance with the Voting Rights Act, redistricting is typically guided by a set of traditional principles that vary by state. These include compactness (districts should be reasonably shaped rather than sprawling or contorted), contiguity (all parts of a district must be connected), preservation of political subdivisions (districts should respect county, city, and town boundaries to the extent feasible), preservation of communities of interest (districts should keep together groups of people who share common concerns, such as economic interests, social characteristics, or geographic features), and preservation of the cores of existing districts (to minimize disruption to existing representational relationships).
These criteria serve as constraints on the redistricting authority's discretion, but they often conflict with one another and with political objectives. A perfectly compact district may split communities of interest; a district that preserves political subdivisions may not achieve population equality without irregular shapes. The relative weight given to these criteria — and whether partisan advantage is treated as a permissible or impermissible consideration — varies by state and by the entity responsible for drawing the maps.
The increasing sophistication of redistricting technology has made it possible to optimize maps for virtually any combination of criteria, including partisan advantage. Algorithms can generate thousands of possible maps and evaluate each one against multiple metrics simultaneously. This same technology, however, can also be used to evaluate whether a particular map is an outlier relative to the universe of possible maps that comply with traditional criteria — an approach that has been used in litigation to demonstrate that a challenged map was designed to achieve partisan ends rather than to serve legitimate redistricting objectives.
Prison Gerrymandering and Other Emerging Issues
Prison gerrymandering refers to the Census Bureau's practice of counting incarcerated persons as residents of the prison facility rather than their home address. Because prisons are disproportionately located in rural areas, this practice inflates the population — and thus the political representation — of the rural districts where prisons are located, while correspondingly diminishing the representation of the urban communities from which most prisoners originate. The distortion is compounded by the fact that incarcerated persons cannot vote in most states, meaning that the population credited to the prison district consists largely of people who have no political voice within it.
Several states have adopted laws requiring that incarcerated persons be counted at their pre-incarceration address for redistricting purposes, including California, Colorado, Connecticut, Delaware, Maryland, Nevada, New Jersey, New York, Virginia, and Washington. The Census Bureau itself considered and rejected changing its methodology for the 2020 census, leaving the adjustment to individual states. The issue illustrates the broader principle that technical choices in how population is counted and allocated can have significant consequences for political representation.
Redistricting after the 2030 census will confront additional challenges, including the growing prevalence of partisan polarization that makes map-drawing increasingly contentious regardless of the process used, the impact of demographic shifts on the Voting Rights Act's requirements for minority-opportunity districts, and the consequences of the Supreme Court's decisions narrowing both the scope of the Voting Rights Act and the availability of federal judicial review for partisan gerrymandering claims. Whether independent commissions, state court litigation, or congressional action will prove the most effective mechanism for addressing these challenges remains to be determined by the political dynamics of the coming decade.