Picture a map of your state divided into congressional districts. Those lines weren’t handed down from the founders or drawn by some neutral algorithm in the sky. Someone sat down and decided them — usually state legislators, sometimes a commission, occasionally a court when things get messy.
Every ten years, after the census tallies up where Americans actually live, states redraw these boundaries. The goal is simple: each district should have roughly the same number of people so every vote carries equal weight. The execution? Well, that’s where geometry meets politics.
Why We Redistrict Every Ten Years
The U.S. Constitution requires a census every decade to count the population. When people move — from cities to suburbs, from one state to another — the math changes. A state that gained 500,000 residents might gain a congressional seat. One that lost population might lose a seat.
After the 2020 census, Texas gained two seats and Colorado, Florida, Montana, North Carolina, and Oregon each gained one. Meanwhile, California, Illinois, Michigan, New York, Ohio, Pennsylvania, and West Virginia each lost a seat. Those seats have to come from somewhere and go somewhere — which means new maps.
But even states that don’t gain or lose seats still redraw their internal lines. If half your population moved from rural counties to urban ones over the past decade, your districts need to rebalance so each one still contains roughly equal numbers of people. In 2020, that magic number was about 761,000 people per district.
Who Actually Draws the Lines
In most states, the state legislature draws congressional maps just like they’d pass any other law — both chambers vote, the governor signs or vetoes. Thirty-three states used this approach after the 2020 census.
Seven states only have one congressional district (Alaska, Delaware, North Dakota, South Dakota, Vermont, and Wyoming), so there’s nothing to draw. Montana went from one district to two after 2020, so they joined the redistricting club for the first time in decades.
The rest use some form of commission — groups designed to take the pen out of legislators’ hands. These vary wildly. Some are advisory (they draw maps but the legislature still votes). Some are independent (they draw the maps and that’s that). Some are politician commissions (legislators draw their own districts but do it in a separate committee). Some are citizen commissions (regular people, not elected officials).
California, for example, uses a 14-member citizen commission picked through an application process. Iowa has a nonpartisan legislative services agency draw maps that the legislature can only approve or reject, not amend. New York tried a commission after 2020, but when it deadlocked, the legislature drew the maps anyway — which ended up in court, leading to new maps drawn by a court-appointed expert.
And when states can’t agree or maps violate state or federal law, courts step in as the map-drawers of last resort.
The Rules of the Road
Federal law sets a few hard requirements. Districts must be roughly equal in population — the Supreme Court has said they can’t vary by more than a tiny percentage. Districts can’t dilute the voting power of racial minorities, per the Voting Rights Act. That’s about it from Washington.
State constitutions and laws add their own requirements. Some states require districts to be geographically compact (no wildly sprawling shapes). Some say districts should keep communities of interest together — meaning cities shouldn’t be split unnecessarily, or counties should stay whole when possible. Some prohibit drawing maps to favor or hurt a political party.
But here’s the thing: many of these requirements are vague, contradictory, or unenforceable. What counts as “compact”? What’s a “community of interest”? When states write that districts should “respect municipal boundaries where practicable,” that word practicable leaves a lot of room for interpretation.
When Map Drawing Becomes Gerrymandering
The term comes from Elbridge Gerry, an early Massachusetts governor whose party drew a district so contorted it supposedly looked like a salamander. A political cartoonist dubbed it a “Gerry-mander” in 1812, and the name stuck.
Gerrymandering means drawing districts to advantage one group over another. The two classic tactics are packing and cracking. Packing concentrates opposition voters into a few districts they’ll win overwhelmingly, wasting their votes beyond what’s needed to win. Cracking splits opposition voters across many districts so they don’t have a majority in any of them.
Say you have a state with 60% blue voters and 40% red voters, and you need to draw five districts. If you drew them proportionally, you’d expect three blue districts and two red ones. But if the blue party controls redistricting, they might pack red voters into one district they’ll win 90-10, then spread blue voters across the other four districts to win each 55-45. Final score: 4-1 instead of 3-2. Flip the mapmaker and the same thing happens in reverse.
Modern mapping software makes this easier than ever. Mapmakers can pull up data down to the city block — party registration, past election results, demographics, even consumer data. They can test thousands of scenarios to see which configuration produces the best results for their side.
What Courts Can and Can’t Do About It
In 2019, the Supreme Court ruled in Rucho v. Common Cause that federal courts can’t police partisan gerrymandering. The Court said these are “political questions” beyond the reach of federal judges — there’s no clear constitutional standard for when partisan mapmaking goes too far.
But that doesn’t mean anything goes. Federal courts still enforce the equal population requirement and the Voting Rights Act’s protections against racial discrimination in redistricting. And state courts can still strike down maps under state constitutions. In the 2021-2022 redistricting cycle, state supreme courts in North Carolina, Ohio, Pennsylvania, and New York all rejected maps, some multiple times.
When courts throw out maps, they either send them back to the legislature for another try or appoint a special master to draw new ones. Sometimes this happens so close to an election that states have to delay primaries or scramble to implement new maps in a matter of weeks.
Why These Lines Shape Everything
Congressional districts determine who can run where, who your neighbors are politically speaking, and which voters each representative needs to listen to. In a competitive district, a member of Congress might moderate positions to appeal to swing voters. In a safe district, the real election is the primary, which typically draws more partisan voters.
After the 2022 elections — the first under the new maps — analysts estimated that only about 40 of 435 House districts were truly competitive. Whether that’s because of gerrymandering or because Americans increasingly live near people who vote like they do (geographic self-sorting) is debated. It’s probably both.
The maps drawn after each census last for ten years, barring court intervention. That’s a decade of determining which votes matter in which places, which communities get grouped together, and how responsive representatives need to be to different kinds of voters.
Every line on these maps is a choice someone made. Understanding who makes those choices and under what rules — that’s how you see the structure behind the process, beyond any particular election result.