How Redistricting Works: Drawing Districts, Gerrymandering, and Political Power
Every ten years, following the census, the boundaries of legislative districts across the country are redrawn. That process — redistricting — determines which communities are grouped together for purposes of electing representatives, and it can shift political power dramatically without a single vote being cast. Understanding how it works is fundamental to understanding American electoral politics.
Published June 25, 2026The United States elects most of its federal and state legislators from single-member districts: each geographic district elects one representative, and the candidate who receives the most votes in that district wins. This system means that the drawing of district boundaries is itself a consequential political act. A district that combines a large number of one party's supporters with relatively few of the other's will reliably elect a representative of the first party regardless of statewide vote totals. The party that controls the redistricting process can, within limits, shape a map that advantages its candidates for the decade until the next census.
Who draws the maps
In most states, the state legislature draws congressional and state legislative district maps, and the governor typically has veto authority. This means the party that controls the statehouse after each census controls the maps for the following decade. States have adopted varying rules and criteria for redistricting, but the process is inherently political when the mapmakers are elected officials with an interest in the outcome. The dominant party can draw maps that pack opposition supporters into a small number of heavily lopsided districts or crack opposition communities across multiple districts to prevent them from forming a majority anywhere.
A growing number of states have moved to independent or bipartisan redistricting commissions in response to concerns about partisan gerrymandering. California, Arizona, Michigan, Colorado, and others use commissions whose members are selected through processes designed to reduce partisan control. The design of these commissions varies considerably, as do evaluations of how well they succeed in insulating the process from partisan manipulation. Even ostensibly independent commissions involve human decision-makers who may hold views that affect their choices, and the criteria used to evaluate maps — compactness, preserving political subdivisions, competitive districts — do not always point in the same direction.
The legal constraints on redistricting
The constitutional requirement that congressional districts within each state have equal population derives from the Supreme Court's one-person-one-vote decisions in the 1960s. Baker v. Carr and Reynolds v. Sims established that the equal protection clause requires legislative districts to have substantially equal populations, ending a system in which rural districts with far fewer voters than urban districts had equal representation. Today, congressional districts must be nearly exactly equal in population; state legislative districts can deviate more but must be substantially equal.
The Voting Rights Act imposes additional requirements. Section 2 prohibits voting practices, including redistricting plans, that discriminate on the basis of race. Where minority voters are sufficiently numerous and geographically compact, and where racially polarized voting patterns exist, the act can require drawing districts in which minority voters have the opportunity to elect their preferred candidates. These majority-minority districts have been both required by the Voting Rights Act in some circumstances and subjected to constitutional limits when race is deemed too predominant a factor in their drawing.
Partisan gerrymandering and the courts
The Supreme Court addressed the question of partisan gerrymandering — drawing maps to favor one political party — directly in the 2019 Rucho v. Common Cause decision. The court held that partisan gerrymandering claims present a political question beyond the reach of federal courts: there is no judicially manageable standard for determining when partisanship in redistricting has gone too far, because the Constitution does not mandate any particular level of partisan fairness in district maps. Federal courts therefore cannot hear challenges to redistricting plans based solely on partisan gerrymandering.
The Rucho decision left open challenges under state constitutions, and state courts have been more willing to engage with partisan gerrymandering claims under state constitutional provisions. Several state supreme courts have struck down maps as unconstitutional partisan gerrymanders under state law, and several state legislatures have responded to those rulings with new maps or with challenges to the courts' authority to impose redistricting requirements.
Racial gerrymandering in the current environment
The interaction between racial and partisan considerations has become among the most complex areas of redistricting law. Because race and party are often highly correlated — Black voters in particular vote overwhelmingly for Democratic candidates in most states — drawing maps to minimize minority representation and drawing maps to minimize Democratic representation can achieve similar results through technically different means. Courts have had to grapple with whether a challenged map was drawn with race as the predominant factor, which is constitutionally suspect, or with partisan considerations that happened to affect minority communities, which is not reachable in federal court after Rucho.
The decade following the 2020 census produced extensive redistricting litigation, including Supreme Court cases addressing Alabama's and South Carolina's congressional maps. The outcomes of these cases, combined with the weakened preclearance requirements after Shelby County v. Holder, have reshaped the legal landscape for racial redistricting in ways that are still being worked out through ongoing litigation and legislative responses. The political stakes of redistricting ensure that each new decade brings fresh controversies to courts, commissions, and legislatures across the country.