Redistricting, Explained

The lines on a map decide which voters pick which member of Congress. Here's how those lines get drawn, and why a few of them can decide who controls the House.

Every ten years, after the U.S. Census, every state has to redraw the lines that decide which voters belong to which voting district. That process is called redistricting. It sounds boring. It is not. The lines on those maps decide which party wins Congress as much as the actual votes do.

What's a District?

A congressional district is just a chunk of a state. Each district elects one person to the U.S. House of Representatives. There are 435 districts in total, one for every House seat. The size of a district is based on population, not land. A district in New York City might cover a few neighborhoods. A district in Wyoming covers the whole state.

State legislatures also have districts for their own state senators and state representatives. Same idea, smaller scale.

Why Every Ten Years?

The U.S. counts its people every ten years in something called the Census. Between counts, populations shift: people move, cities grow while rural areas shrink. After each Census, two things have to happen:

Reapportionment. States that gained a lot of people get more House seats. States that lost people lose seats. The total stays at 435.
Redistricting. Every state then redraws its district lines so each district has roughly the same number of people inside it. That part is required by federal law (it's called "one person, one vote").

The most recent Census was in 2020. The next one is in 2030. So the maps states are using right now were drawn in 2021 or 2022, and they're supposed to stay in place until after 2030.

Who Actually Draws the Lines?

It depends on the state. Most of them give the job to their state legislature. A few states have realized that's a bad idea (more on that in a second) and have set up independent commissions instead.

State legislature draws the map

This is how most states do it. The party in charge of the legislature draws the lines, the governor signs off (or doesn't), and the courts can step in if anyone sues. The party in power tends to draw maps that help itself. That's where gerrymandering comes from.

Independent commission draws the map

States like California and Michigan (Arizona too) use citizen commissions made up of regular people from both parties, plus unaffiliated voters. The idea is to take the pen away from the politicians who benefit. Maps from these commissions tend to be less skewed, though no system is perfect.

A court draws the map

Sometimes the legislature can't agree, or a judge throws out the map they came up with. In those cases, a court can step in and draw the lines itself, often using a court-appointed expert called a special master.

What's Gerrymandering?

Gerrymandering is when whoever's drawing the map draws the lines on purpose to help one side win more seats. It's named after a Massachusetts governor in 1812 who signed off on a district shaped like a salamander to help his own party. The press called it a "Gerry-mander," and the name stuck.

There are two main tricks:

Packing

Cram as many of the other party's voters as possible into a few districts. They'll win those districts by huge margins, but those wasted votes can't help them anywhere else. Think of it as putting all your opponent's points on one scoreboard.

Cracking

Split the other party's voters across many districts so they're a minority in each one. They lose every district by a little instead of winning a few by a lot. Think of it as spreading your opponent's points so thin that none of them count.

Done well, gerrymandering can let a party that gets fewer total votes still win more seats. That's not a hypothetical. It happens in real elections.

Is Gerrymandering Legal?

Some kinds, no. Other kinds, yes.

Drawing lines based on race is illegal under federal law. The Voting Rights Act says you can't carve up neighborhoods to dilute the political power of minority voters. Federal courts can throw out maps that do this, and they have, many times.

Drawing lines for political reasons is something the U.S. Supreme Court ruled in 2019 (Rucho v. Common Cause) that federal courts can't fix. That decision left it up to state courts and state laws to handle partisan gerrymandering on their own. Some states have stepped up. Many haven't.

Mid-Decade Redistricting

Most of the time, states draw their maps once a decade and leave them alone until the next Census. Redrawing in the middle of the decade is rare. There's usually no reason to bother, since the existing map already reflects the most recent population count.

But it does happen, especially when the political stakes are high enough. In 2025 and 2026, several states have tried it. Texas Republicans drew a new map that helps them win more seats. Virginia voters approved a new map that helps Democrats win more seats. California did the same on the Democratic side a few months earlier. Each side argues the other started it.

Mid-decade redraws aren't automatically illegal, but they almost always end up in court. State constitutions and federal voting laws (including the Voting Rights Act) give people plenty to sue over.

Why This Matters for Your Vote

Most House districts aren't really competitive anymore. Out of 435, only about 30 to 40 are genuinely up for grabs in any given cycle. The rest are baked in by the way the lines are drawn. Whichever party "owns" a district wins it cycle after cycle, often by 20 points or more.

That has a few real consequences:

Primaries matter more than general elections in safe districts. If your district is locked in for one party, the real fight is the primary, where you pick that party's nominee. Primary turnout is usually low, so a small group of voters often picks who represents a much bigger one.
The "national vote" doesn't always match the seat count. A party can win more total votes for the House across the whole country and still end up with fewer seats, because of how the lines are drawn.
Where you live changes how much your vote moves the needle. A vote in a Toss-Up district has a big effect on who wins. A vote in a Safe district mostly matters in the primary.

How to Tell if Your District Was Gerrymandered

There's no perfect test, but here are some clues:

It looks weird on a map. Long, snaking districts with strange shapes are a classic sign. A district shouldn't look like a salamander or a barbell.
One party wins by huge margins every cycle. If your district is winning by 30+ points for the same party every two years, it was probably drawn that way on purpose.
The state's overall vote doesn't match the seats. If your state splits roughly 50/50 between the parties statewide but one party wins 70 percent of the House seats, something's off.

The Princeton Gerrymandering Project and Ballotpedia both keep public maps and analysis. If you're curious about your own district, that's where to look.

The Bottom Line

Redistricting is one of the most important things in American politics that almost nobody pays attention to. The lines on a map can decide which party wins Congress before a single voter shows up. That's why both parties fight so hard over them, and why even technical-sounding court rulings on redistricting are worth following.

For news on what's happening right now, see our article on the 2026 Supreme Court rulings on Texas and Virginia.

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