What is gerrymandering? How district lines shape elections

Gerrymandering is drawing the boundaries of election districts to give one party or group an advantage it wouldn't win with fair lines. Map-drawers do it mainly two ways: packing the other side's voters into a few districts it wins by huge margins, and cracking the rest across many districts where they fall just short. The voters stay the same; the lines decide how many seats their votes are worth.

In short

• Districts are redrawn after every census so each holds about the same number of people, and in most states the legislature draws them, which invites self-interest.
• With the same voters, different maps can produce very different results, as the worked example below shows.
• Since 2019, federal courts don't hear claims that a map is too partisan; state courts, state constitutions and independent commissions are where the limits now come from.

Where does the word come from?

From a salamander. In 1812, Massachusetts redrew its state senate districts to help the governor's party, and one district north of Boston, in Essex County, curled into a long, winding shape. On 26 March 1812 the Boston Gazette ran a cartoon by the engraver Elkanah Tisdale that gave the district wings, claws and a head and named it "The Gerry-mander", after Governor Elbridge Gerry, who had signed the plan. According to the Library of Congress, Gerry privately found the plan "highly disagreeable" but signed it anyway. He lost the next election, while his party kept control of the state senate the new map was drawn for. He later became vice president under James Madison.

The practice is older than the word, and both major parties have used it ever since. It is legal in itself: drawing lines is unavoidable, and every line helps someone.

How does redistricting work?

Every ten years the census counts the population, and the 435 seats in the House of Representatives are shared out among the states. Each state then redraws its districts so that each holds roughly the same number of people. The Supreme Court made that a rule in the 1960s with the principle of "one person, one vote", which requires near-equal populations in congressional districts and state legislative districts alike. After the 2020 census, the average congressional district held 761,169 people.

In most states, the state legislature draws the maps and the governor can sign or veto them, as with any law. That means the politicians whose seats depend on the lines usually draw them. A party that controls the legislature and governorship in a redistricting year can shape a decade of elections for Congress and for the legislature itself.

How do packing and cracking work?

The easiest way to see it is with a small made-up state: 50 voters, 5 districts of 10 voters each. Thirty voters, 60%, support the Blue party, and 20, 40%, support Red. Here are three legal maps of the same voters.

District	Map A: Blue sweeps	Map B: roughly proportional	Map C: Red packs and cracks
1	6 Blue, 4 Red: Blue	10 Blue: Blue	10 Blue: Blue
2	6 Blue, 4 Red: Blue	10 Blue: Blue	10 Blue: Blue
3	6 Blue, 4 Red: Blue	6 Blue, 4 Red: Blue	4 Blue, 6 Red: Red
4	6 Blue, 4 Red: Blue	2 Blue, 8 Red: Red	3 Blue, 7 Red: Red
5	6 Blue, 4 Red: Blue	2 Blue, 8 Red: Red	3 Blue, 7 Red: Red
Seats	Blue 5, Red 0	Blue 3, Red 2	Blue 2, Red 3

With 60% of the votes, Blue can win all five seats or only two, depending on where the lines go. Map A cracks Red's 40% across every district, so Red wins nothing. Map C packs 20 Blue voters into two districts Blue wins 10 to 0, then cracks the other 10 Blue voters across three districts that Red wins narrowly.

One way to measure this counts "wasted" votes: every vote for a losing candidate, plus every vote for a winner beyond half of a 10-voter district, which is 5. Under Map C, Blue wastes 5 votes in each of districts 1 and 2 and all 10 of its votes in districts 3 to 5, which is 20 of its 30 votes. Red wastes only 1, 2 and 2 surplus votes in the districts it wins, which is 5 of its 20. The difference, 15 wasted votes out of 50 cast, is 30%. That measure, the efficiency gap, was proposed by the scholars Nicholas Stephanopoulos and Eric McGhee in 2015 and was argued in court, though no court requires it.

Real maps work the same way on a larger scale, with computers testing thousands of possible lines against precinct-by-precinct voting records. Odd shapes aren't required; a skilled gerrymander can look perfectly tidy.

What do the courts allow?

Federal courts treat two kinds of gerrymandering differently.

Racial gerrymandering, drawing lines mainly by race, can violate the Constitution's equal protection clause, under the 14th Amendment, and the Voting Rights Act of 1965. For decades, Section 2 of that act could require states to draw districts where a minority group could elect its preferred candidates. In Louisiana v. Callais, decided on 29 April 2026, the Supreme Court narrowed that sharply: according to the Congressional Research Service, a Section 2 claim now needs evidence supporting a strong inference of intentional discrimination, and challengers must show that race, not party, explains the voting patterns.

Partisan gerrymandering, drawing lines for party advantage, is another matter. In Rucho v. Common Cause, on 27 June 2019, the Court ruled 5–4 that such claims are a "political question" federal courts cannot decide, while calling extreme partisan gerrymandering "incompatible with democratic principles". The case joined two maps drawn by opposite parties: a Republican-drawn map in North Carolina and a Democratic-drawn map in Maryland. The Court pointed to other remedies: state courts applying state constitutions, as Pennsylvania's Supreme Court did when it struck down the state's congressional map in 2018, Congress, and voters creating commissions.

What reforms have states tried?

The main reform is taking the pen away from legislators. Arizona voters created an independent commission in 2000, California's voters created a citizens' commission for state districts in 2008 and extended it to Congress in 2010, and Michigan's voters created one in 2018. Other states use bipartisan commissions, require public hearings, or ban favoring a party in their constitutions.

Reform can also run the other way. In 2025 and 2026, several states redrew congressional maps in the middle of the decade, not after a census. Texas passed new maps in August 2025; Missouri, North Carolina and Ohio followed that fall, and California's voters approved Proposition 50 in November 2025, which set aside the commission's map for the 2026 to 2030 elections in favor of one drawn by the legislature. Florida and Tennessee redrew in the spring of 2026. Courts, voters and legislatures stopped other attempts, in Virginia and Indiana among others, according to the Voting Rights Lab's tracker as updated on 19 August 2026. These maps changed fast, so any count of them needs its date.

Still argued

How far map-drawing should be taken out of politics is argued. Supporters of independent commissions say legislators shouldn't choose their own voters, that commissions produce more competitive districts, and that public trust depends on it. Critics say commissions are not truly free of politics, that their members and staff have views too, that line-drawing always involves value choices courts and voters should leave to elected officials, and that one state disarming while others don't simply hands seats to the other party, which is the argument made for the mid-decade redraws of 2025. Political scientists also note that some imbalance comes without any gerrymander, because one party's voters cluster in cities, which packs them naturally.

Gerrymandering shapes the House more than the presidency: the Electoral College counts statewide votes in all but two states, so district lines barely touch it. It shapes every House election, including the midterm elections, when the House is at the top of the ballot with no presidential race above it. And it raises a question every democracy with districts has to answer: who should draw the lines.

Check yourself

• Without looking back: explain packing and cracking, using the 50-voter example.
• Why do federal courts hear claims of racial gerrymandering but not partisan gerrymandering?
• What is an independent redistricting commission meant to fix, and what do its critics say?

Sources

• Gerrymandering: The Origin Story — Library of Congress, 2024
• Rucho v. Common Cause, No. 18-422 — Supreme Court of the United States, 2019
• Gerrymandering Explained — Brennan Center for Justice, updated 2026
• Congressional Redistricting: High Court Narrows Voting Rights Act in Louisiana v. Callais — Congressional Research Service, 2026
• An Emerging Trend: Mid-Decade Redistricting — Voting Rights Lab, 2026
• U.S. Census Bureau Today Delivers State Population Totals for Congressional Apportionment — U.S. Census Bureau, 2021