What Is Gerrymandering and How Does It Work?

Gerrymandering is the drawing of electoral district boundaries to give one party an unfair advantage, and once you understand the trick, you start seeing it everywhere in American politics. The votes are still counted fairly on election day. The problem happens earlier, when someone decides which voters get grouped together, because that grouping can decide most contests before a single ballot is cast.

That is the short answer to what is gerrymandering and how does it work. The longer answer matters, because the same word covers three different games, a set of court rules that changed in 2019 and again in 2026, and a map fight that is still reshaping the House of Representatives as Americans vote in the 2026 midterms. This guide explains all of it in plain English, with a worked example you can check with simple arithmetic.

Redistricting First: Why the Lines Have to Move at All

Every ten years, the US Census counts the population, and the 435 seats in the House of Representatives are reapportioned among the states based on where people now live. Each state must then redraw its congressional districts so that each one holds roughly the same number of people, about 760,000 after the 2020 Census. State legislatures do the same for their own state house and state senate districts.

Redrawing is unavoidable, because people move. A district drawn in 2010 for a fast-growing suburb and a shrinking rural county would be badly out of balance by 2020. The question is never whether the lines move. The question is who holds the pen, and what rules they have to follow.

In most states, the legislature draws the lines, usually subject to the governor’s veto, which is why redistricting feels so political. A growing number of states use commissions instead: some are advisory, some are bipartisan panels of party appointees, and a few, like Michigan’s citizen commission created by voters in 2018, exclude current officeholders entirely. Iowa uses a nonpartisan staff model, and in some states courts step in when politicians deadlock. The system you live under depends entirely on your state, which is one reason national maps look so inconsistent.

Four basic rules are supposed to constrain every mapmaker. Districts must have nearly equal populations, under the Supreme Court’s one person, one vote principle from Reynolds v. Sims (1964). They must be contiguous, meaning all parts connected, not scattered islands. They are supposed to be reasonably compact, rather than stretched into bizarre shapes. And they are supposed to respect communities of interest, keeping neighborhoods, counties, and towns together where possible. On top of that, the Voting Rights Act of 1965 bars maps that dilute the voting power of racial minorities. Notice what is missing from that list: there is no federal rule that says a map must be fair to both parties.

What Is Gerrymandering and How Does It Work? Packing and Cracking

Almost every gerrymander is built from just two moves, and a simple example shows how powerful they are. Imagine a small state with 50 voters, 30 supporting Party A and 20 supporting Party B, divided into five districts of 10 voters each. If the districts reflected the vote, Party A would win three seats and Party B would win two.

Now let Party A draw the map. It packs Party B’s voters into a single district, 10 to 0, so Party B wins that seat by a landslide and wastes votes on a margin it did not need. Then it cracks the remaining 10 Party B voters across the other four districts, about two or three per district, so Party B falls just short in each one. Result: Party A wins four of five seats, 80 percent of the seats, with 60 percent of the vote.

Flip the pen and the trick works in reverse. Party B packs Party A’s voters into two districts, 10 to 0 each, then splits the remaining 10 Party A voters across three districts, about three per district, against seven Party B voters. Result: Party B wins three of five seats, 60 percent of the seats, with only 40 percent of the vote. Same voters, same state, completely different legislature, and the only thing that changed was where the lines fell.

Real maps are more complicated, because mapmakers now use precinct-level voting history and software that can test thousands of map variants in minutes. But the logic is identical. Wasted votes are the currency: every vote above the bare majority needed to win a district, and every vote cast for a losing candidate, is a vote that bought no seat. A good gerrymander wastes the other side’s votes and conserves its own, which is why analysts measure maps with tools like the efficiency gap, a simple count of each party’s wasted votes.

Where the Strange Word Came From

The word is older than most people expect, and it started as a joke. In 1812, Massachusetts Governor Elbridge Gerry signed a redistricting bill that created a state senate district in Essex County so twisted that the Boston Gazette printed a cartoon of it with wings and claws, calling it a Gerry-Mander, after the salamander it resembled. The cartoon, drawn by Elkanah Tisdale, stuck, and so did the practice. Gerry himself lost his re-election bid that year, but his party kept the senate seats the map was drawn to hold.

The practice is older than the name. In Virginia, Patrick Henry tried to draw the state’s first congressional map in a way that would keep James Madison out of Congress. Madison won anyway, which is a useful reminder: a gerrymander tilts the odds, it does not guarantee the result. Voters can still surprise a map, especially when turnout shifts or a scandal changes a race.

Three Kinds of Gerrymander, and Why the Distinction Matters

People use one word for three different games, and courts treat them very differently, so it helps to separate them.

Partisan gerrymandering is the familiar kind: lines drawn to help one party win more seats than its vote share would suggest. Both parties do it when they hold the pen, and both have defended it when it helped them. Texas redrawing its map in 2025 to add Republican seats, and California suspending its independent commission in 2025 to draw a map favoring Democrats, are the same move in opposite colors.

Racial gerrymandering is lines drawn to increase or decrease the electoral influence of a racial group. This has a long American history, from maps that split Black communities across several districts to maps that packed Black voters into a single district to limit their influence elsewhere. It is also the kind courts have policed most actively, because the Constitution and the Voting Rights Act speak directly to race in a way they do not speak to party.

Incumbent protection is the quiet third kind, sometimes called a bipartisan gerrymander. Here both parties agree to draw safe districts for current officeholders, regardless of party, so almost nobody faces a real challenge. Voters get less choice, challengers get no opening, and the legislature barely changes even when public opinion does. A map can be an incumbent protection gerrymander even if the statewide seat split looks roughly proportional.

What the Courts Will and Will Not Do

For decades, the Supreme Court struggled with partisan gerrymandering, and in 2019 it effectively gave up on policing it at the federal level. In Rucho v. Common Cause, which examined North Carolina’s map, the Court held that claims of partisan gerrymandering present political questions beyond the reach of federal courts, even while calling gerrymandering inconsistent with democratic principles. In practice, that means a voter who believes a map is unfair because of party alone has no federal court remedy. State courts are a different story: several state constitutions ban partisan gerrymandering outright or guarantee free elections, and state supreme courts have struck down maps under those provisions, most famously in Pennsylvania in 2018.

Racial gerrymandering remains challengeable, but the ground shifted again in 2026. In Louisiana v. Callais, decided on April 29, 2026, the Supreme Court found that Louisiana’s creation of two Black-majority districts in 2024 had violated Section 2 of the Voting Rights Act because it purposefully reduced the voting power of white voters, reversing a lower court that had found a single Black district violated Section 2 by diluting Black voting power. Commentators noted that the ruling raised the bar for racial gerrymandering challenges by putting more weight on proof of discriminatory intent. The practical effect is still being litigated state by state, but mapmakers and challengers alike are now reading every new map through that decision.

Two older cases still frame the basics. Reynolds v. Sims requires roughly equal populations, so a map cannot simply give rural districts far fewer people than urban ones. And the Voting Rights Act still requires states to consider whether a map denies minority voters an equal opportunity to elect candidates of their choice, a test that turns on voting patterns and history in each state, not on a single national formula.

Why 2025 and 2026 Became a Map Fight Again

Redistricting used to happen once a decade, after the census. That norm has broken down. Since 2020, more than a quarter of all congressional seats have been redrawn mid-decade, and the 2025 to 2026 wave is the reason this topic is back in the news.

It started in Texas, where President Donald Trump endorsed redrawing the state’s maps in 2025, saying Republicans were entitled to five more seats. California answered with Proposition 50, approved by voters in a November 2025 special election with 64 percent of the vote, which temporarily suspended the state’s independent commission and allowed a map favoring Democrats. Missouri, North Carolina, Ohio, and Utah also changed their maps, while Maryland’s plan failed in the legislature. Virginia voters approved a new House map in April 2026 that could have added Democratic seats, but the state’s supreme court struck it down the following month on procedural grounds, holding that the approval process violated the state constitution. In April 2026, Florida’s legislature approved a map proposed by Governor Ron DeSantis that could add as many as four Republican seats, and it faces a likely court challenge under a Florida constitutional provision that bars redrawing boundaries for purely political gain. After the Callais ruling, Louisiana delayed its planned May primary by two months to redraw its maps, and Tennessee approved a map eliminating its only Democratic-held House seat.

The pattern is worth noting, because it cuts across party lines. When one side redraws mid-decade, the other side answers with its own redraw, and voters end up choosing representatives under maps drawn for the next election, not the last census. That tit-for-tat cycle is exactly what the once-a-decade norm was supposed to prevent, and its breakdown is why several states are voting in the 2026 midterms under lines that did not exist two years ago.

How to Tell if Your Own District Is Gerrymandered

You do not need a statistics degree to spot a suspicious map. Run these five checks on your own district.

First, look at the shape. A district that snakes across a state, sprouts narrow corridors, or wraps around a city like a donut is a warning sign, though geography alone is not proof: rivers, coastlines, and county lines create odd shapes too. Second, check the margins. If your representative routinely wins by 30 points or more, and the same party has held the seat for decades, the district may have been drawn to be safe rather than competitive. Third, compare votes and seats statewide. If a party wins about half the statewide House vote but only a third of the seats, or vice versa, the map deserves a closer look. Fourth, check whether your community is split. If your town, school district, or neighborhood is divided among two or three representatives, while a similar community nearby stays whole, ask why the line fell there. Fifth, check whether your district changed without you moving. If a redraw moved you to a new representative even though your address stayed the same, look at what changed around you and which party gained from it.

For a deeper check, free tools do the arithmetic for you. Dave’s Redistricting App lets you draw and compare maps, PlanScore scores real maps for partisan bias, and All About Redistricting, run by Loyola Law School professor Justin Levitt, tracks who draws the lines in every state and what the rules are. If several of these checks point the same way, you are probably looking at a gerrymander, not a coincidence.

What Gerrymandering Changes in Your Daily Life

The most important effect is also the least visible: safe seats move the real election from November to the primary. When a district is drawn so that one party cannot lose the general election, the only contest that matters is that party’s primary, where turnout is lower and voters tend to be more ideological. Representatives in safe seats have little incentive to appeal to the middle, and a strong incentive to avoid any vote that could draw a primary challenger. That is how a legislature can drift away from the views of the broader public even while every member was duly elected.

It also changes what your representative does for you. A member in a competitive district works hard to keep swing voters happy, answers constituent mail promptly, and thinks twice before taking an extreme position. A member in a safe district can ignore the other party’s voters in the district entirely, because they cannot threaten re-election. Over time, that breeds the cynicism you hear in conversations about politics: the feeling that the outcome was decided when the map was drawn, not when the votes were counted.

One common misunderstanding is worth correcting. Gerrymandering affects district races: the House, state legislatures, and city councils. It does not affect statewide races, because a governor, a senator, or a presidential candidate runs statewide, and no district line can change a statewide vote total. That is why a state can have a heavily gerrymandered House map and still elect a governor from the other party. Your vote always counts in statewide races, and in a district race it counts most when the district is competitive, which is precisely what a gerrymander tries to prevent. For context on how the rest of the system fits together, see our guides on how the Electoral College works and how midterm elections work.

Fixes That Are Actually Being Tried

The fixes are known, and none of them adopts itself, because the people who benefit from a gerrymander are usually the people who would have to vote to end it. Independent citizen commissions take the pen away from legislators, and Michigan, Arizona, and California have all used versions of them, though California’s 2025 suspension shows a commission lasts only as long as the politics around it. State constitutional bans give state courts a clear standard to enforce, as Pennsylvania’s free-elections clause did in 2018. Some reformers push for ranked-choice voting or multi-member districts with proportional rules, which would make the lines matter far less, because several representatives would be elected from a larger area in proportion to the vote. Those ideas are rarely adopted, for the obvious reason that they reduce the advantage of whoever is currently winning.

The realistic path, historically, has been voters acting directly: ballot initiatives creating commissions, state constitutional amendments, and lawsuits under state constitutions. Where reform has worked, it has usually happened because voters took the pen out of politicians’ hands themselves, rather than waiting for politicians to hand it over.

Frequently Asked Questions

Is gerrymandering illegal?

It depends on the kind. Racial gerrymandering can violate the Constitution and the Voting Rights Act, and partisan gerrymandering can violate some state constitutions. But after Rucho v. Common Cause in 2019, partisan gerrymandering alone is not a claim federal courts will decide, so a purely partisan map can be legal under federal law even if it is widely seen as unfair.

Does gerrymandering happen in both parties?

Yes. Whichever party controls the redistricting process in a state has the same incentive to draw favorable lines, and both parties have done it, in different states and in different decades. North Carolina’s maps have been redrawn in both directions over the past decade, and the 2025 to 2026 wave includes Republican-led redraws in Texas and Florida and a Democratic-led redraw in California.

Can maps change between censuses?

Yes, if state law allows it. Mid-decade redistricting used to be rare, but it is now common: Texas redrew in 2003 and again in 2025, and several states redrew in 2025 and 2026 ahead of the midterms. Some states ban it in their constitutions, and courts can block a redraw that violates state procedure, as Virginia’s supreme court did in 2026.

Does my vote still count if my district is gerrymandered?

Yes, but its power is reduced in that district race. Your vote still counts fully in statewide races for governor, senator, and president, and it still counts in your district race, especially if turnout shifts or the map is redrawn. A gerrymander makes a seat harder to flip, not impossible to flip, and maps have been overturned by courts, ballot initiatives, and voter backlash.

What is the difference between gerrymandering and redistricting?

Redistricting is the neutral process of redrawing district boundaries after the census so districts have equal populations. Gerrymandering is redistricting done with the intent to favor a party, a racial group, or incumbents. Every gerrymander is a redistricting, but not every redistricting is a gerrymander.

Conclusion

Gerrymandering is the manipulation of district boundaries to advantage a party, a group, or incumbents, built from two simple moves, packing and cracking, that waste the other side’s votes and conserve your own. It is not the same as redistricting, it is policed differently depending on whether race or party is involved, and after the Supreme Court’s 2019 and 2026 rulings, most of the fight now happens in state courts, ballot initiatives, and state constitutions. The next time you look at a strange district shape on a map, check its margins, check whether your community is split, and compare the statewide vote with the statewide seats. If the lines explain the result better than the voters do, you have found the trick, and knowing how it works is the first step toward changing it.