What is redistricting?

Redistricting is the process of redrawing the geographic boundaries of electoral districts to reflect population changes, typically conducted after each ten-year census. In the United States, redistricting affects U.S. congressional districts, state legislative districts, and many local districts including city council districts and school board districts.

Federal law requires that congressional districts within each state contain roughly equal populations, a principle called one person, one vote that the Supreme Court established in Wesberry v. Sanders (1964). After each census reveals population growth and shifts, congressional districts must be redrawn to ensure equal population. Population shifts within a state can require significant redistricting even if the state's total number of seats does not change. State legislative districts are similarly subject to one person, one vote requirements, established in Reynolds v. Sims (1964).

Who controls redistricting varies by state. In most states, redistricting is controlled by the state legislature, which passes a redistricting map as ordinary legislation, with the governor able to sign or veto. In states with one-party control of state government, the controlling party often draws maps that favor its candidates, a practice called partisan gerrymandering. Some states use independent redistricting commissions designed to reduce partisan influence. California, Arizona, Michigan, Colorado, and others use independent commissions composed of citizens from both parties and independents. Iowa uses a nonpartisan staff to draw initial maps that the legislature must accept or reject without amendments. Other states use political commissions made up of legislators or other officials from both parties.

Federal law also imposes requirements on redistricting under the Voting Rights Act of 1965. Section 2 of the act prohibits voting practices, including district lines, that have a discriminatory effect on minority voters. The Supreme Court has generally upheld these requirements, though specific applications have been heavily contested. The Court has also held that partisan gerrymandering claims are not justiciable in federal court (Rucho v. Common Cause, 2019), meaning federal courts cannot strike down maps for being too partisan, though state courts can do so under state constitutions.

Recent redistricting cycles have seen significant litigation, with maps in many states subject to multiple rounds of court review. Highly gerrymandered maps drawn for partisan advantage have been struck down by state courts in states such as North Carolina and Pennsylvania based on state constitutional provisions. The decennial redistricting process has substantial implications for which party controls the U.S. House and state legislatures for the next ten years.