Imagine two neighbors who live on the same street and vote the same way, yet their votes carry very different weight because of an invisible line on a map. That line decides who their representative is, and how likely their side is to win.
That is the core of gerrymandering. It is one of the quieter ways the rules of the game can shape the result before a single ballot is cast.
Quick answer: Gerrymandering is drawing voting district boundaries to give one party, group or incumbent an advantage. The main tactics are “packing” (cramming one side’s voters into a few districts) and “cracking” (splitting them across many). Both parties have done it, and reforms range from independent commissions to clearer map-drawing rules.
What Is Gerrymandering, Exactly?
In the United States, voters are grouped into districts, and each district elects a representative. That applies to the U.S. House of Representatives, state legislatures, and many city councils and school boards. Someone has to decide where the lines go.
Gerrymandering happens when those lines are drawn on purpose to help a particular party, candidate or group win more seats than their share of the vote might otherwise produce. The shorthand is memorable: in a normal election, voters choose their politicians. In a gerrymandered one, the map-drawers help choose which voters get which politicians.
The word itself dates to 1812. Massachusetts Governor Elbridge Gerry signed a state senate map with an oddly shaped district, and a newspaper cartoon compared it to a salamander. “Gerry” plus “salamander” gave us “gerrymander.” The tactic is older than the name, and it has never gone away.
Why Do District Lines Exist at All?
The Constitution requires a census every ten years to count the population. That count decides how many seats in the House each state gets. Once a state knows its number of seats, it has to divide its territory into that many districts.
This redrawing process is called redistricting. Districts must be roughly equal in population, a principle often summarized as “one person, one vote,” which the Supreme Court established in a series of rulings in the 1960s. Beyond equal population, the rules get much looser.
In most states, the state legislature draws the maps, usually with the governor’s approval. That detail matters, because it means the people who benefit from the lines are often the people drawing them. If you want the bigger picture of how states and Washington divide authority, our guide to what federalism is and how state and federal power work explains why this job falls to the states.
Packing and Cracking: The Two Core Tactics
Nearly every gerrymander relies on one of two ideas. Both work by wasting the other side’s votes.
Packing
Packing means concentrating as many of the opposing group’s voters as possible into a small number of districts. They win those districts by enormous margins, but every vote beyond what is needed to win is, in a sense, “wasted.” The surrounding districts are then left more favorable to the map-drawers.
Cracking
Cracking means splitting a group of voters across several districts so they never form a majority in any of them. A community that might have won one seat is spread thin enough to lose several.
| Tactic | What it does | Effect on the targeted group |
|---|---|---|
| Packing | Crams a group into a few districts | Wins a few seats by huge margins, loses influence elsewhere |
| Cracking | Splits a group across many districts | Falls short of a majority almost everywhere |
A simple example
Picture a small state with 100 voters, split evenly: 50 who prefer Party A and 50 who prefer Party B. It has five districts of 20 voters each. A fair-looking map might produce a split of seats close to even.
Now imagine the mapmakers favor Party A. They pack 20 Party B voters into one district (a landslide for B), then crack the remaining 30 Party B voters across four districts, about 7 or 8 each, where Party A holds a comfortable majority. Party A wins four of five seats with only half the votes. Nobody changed their mind. Only the lines moved.
Nobody changed their mind. Only the lines moved, and the outcome moved with them.
Both Parties Do It
It is tempting to treat gerrymandering as something only the other side does. The evidence does not support that. When Republicans control the map-drawing process in a state, maps have tended to favor Republicans. When Democrats control it, maps have tended to favor Democrats. Courts and analysts have criticized maps from both parties over the years.
The reason is incentives, not villains. A legislator who draws the maps faces a simple temptation: the rules let you protect your side, your allies and your own seat, and the other party would do the same if it held the pen. In a system where the winner of the last election draws the next map, restraint is costly and rarely rewarded.
Which party benefits in any given decade depends mostly on who held power in which states when the maps were drawn. For more on how incentives shape behavior across institutions, see our explainer on who has power in America and why.
Incumbent protection is a form of gerrymandering too
Not every gerrymander is about one party beating the other. Sometimes the parties cooperate to draw safe seats for sitting officeholders on both sides. Voters get fewer competitive races, and the real contest moves to the primary election, where a smaller and often more committed slice of voters decides the outcome. We will explore that dynamic in our guide to primary elections.
The Racial Dimension and the Law
Gerrymandering has an uncomfortable history connected to race. After the Civil War and Reconstruction, many Southern states used a range of tools to limit Black political power, and district lines were one of them. Packing Black voters into a single district, or cracking them across many, can dilute their influence even when they are numerous.
The Voting Rights Act of 1965 was passed to confront discrimination in voting. Over the decades, courts have applied it to district maps, and the Supreme Court has ruled on cases where race was either used to dilute minority voting power or used too heavily in drawing lines. The legal doctrine here is complicated and has shifted over time, so check current rulings and official sources for the latest. For the deeper historical backdrop, our guide to American history that explains today is a good starting point.
One honest complication is that race and party often overlap in voting patterns. That makes it hard to tell whether a map was drawn to disadvantage a party, a racial group, or both. Courts have wrestled with exactly this question.
What the Supreme Court has said
In 2019, the Supreme Court ruled that claims of partisan gerrymandering raise political questions that federal courts cannot resolve. In plain terms, the justices said there was no workable federal standard for deciding how much partisan advantage is too much. The ruling did not say gerrymandering is good. It said the remedy lies elsewhere, such as state courts, state constitutions, legislatures and voters. To understand how the Court decides these questions, see what the Supreme Court does.
How Do We Know When a Map Is Gerrymandered?
This is harder than it sounds, and it is where disagreement is real. Some warning signs are visible, and others require math.
- Odd shapes. Districts that snake, hook or stretch strangely can signal manipulation, though odd shapes can also come from rivers, coastlines, county lines or the need to keep communities together.
- Seats versus votes. If a party consistently wins far more or far fewer seats than its share of the statewide vote, analysts take notice.
- Statistical tests. Researchers compare a proposed map to thousands of computer-generated alternatives to see whether it is an extreme outlier.
Defenders of existing maps point out that geography matters. Voters of one party are often clustered in cities, which can produce uneven results even when mapmakers act in good faith. Critics respond that this does not excuse maps drawn with partisan intent. Both points can be true at once, which is part of why the question is so hard to settle.
The hardest part is that geography and intent can produce similar-looking maps, and reasonable people disagree about where one ends.
Reform Options and Their Trade-Offs
Because the Supreme Court has stepped back from partisan cases, reform has largely moved to the states. Here are the main approaches, each with real strengths and real limits.
Independent or bipartisan commissions
Some states hand map-drawing to a commission rather than the legislature. Designs vary: some commissions include members of both parties and independents, and some limit who can serve. Supporters say this removes the conflict of interest. Critics worry about who selects commissioners, whether they are truly independent, and whether unelected panels should hold such power. Results have been mixed and depend heavily on design.
Clearer map-drawing rules
Some states require districts to be compact, to keep counties and cities intact, or to respect “communities of interest.” These criteria narrow the room for manipulation, though they can conflict with each other and still leave judgment calls.
State courts and constitutions
Some state constitutions contain provisions that courts have used to strike down maps. This path depends on each state’s own laws and judges.
Ballot initiatives
In several states, voters have changed redistricting rules directly through the ballot. If you are curious how that works, we will cover it in our explainer on ballot initiatives.
Federal legislation
Congress has the power to set rules for House elections, and proposals to require standards or commissions nationwide have been debated for years. Whether that is wise raises a question about the balance of state and national power. For how a proposal like that would travel through Washington, see how a bill becomes a law.
| Reform | Main strength | Main concern |
|---|---|---|
| Independent commission | Reduces self-interest | Selection and accountability questions |
| Map-drawing criteria | Sets visible standards | Criteria can conflict or be gamed |
| State court review | Provides a check | Varies by state; judges face scrutiny too |
| Ballot initiative | Citizens decide directly | Only available in some states |
| Federal rules | Uniform national standard | Federalism and political feasibility |
Where the Disagreements Are Real
It helps to separate three kinds of questions. Facts: lines are drawn by specific people under specific rules, and maps can be measured. Interpretations: whether a given map crosses the line from ordinary politics into manipulation, and how much geography explains. Values: whether competitive districts matter more than stable representation of communities, and who should hold the pen.
Some people favor compactness and strict rules. Others fear that rigid formulas hide their own biases. Some prioritize proportional outcomes, while others prioritize local representation tied to place. These are genuine tensions, not obvious right-or-wrong answers. Our guide to republic versus democracy explores some of the deeper principles behind them.
Think about it: If you could design the process for drawing district lines from scratch, who would you trust to do it, and what safeguards would you want? Would you trade some predictability for more competitive elections, or the other way around? Try asking someone who votes differently than you do how they would answer. If these questions interest you, you might also explore how to run for local office and shape these processes yourself.
What You Can Do
You do not need to be a mapmaker to take part. Redistricting hearings are often public, and many states post proposed maps online. Local officials also draw their own district lines, so the process reaches down to your city council and school board. If you want to understand what those bodies do, see what a city council does.
Look up how your state draws its maps, check whether your district has changed after the last census, and read coverage with care. Our media literacy guide can help you sort analysis from advocacy, and how to talk about politics with family offers ways to discuss this without a fight. Because laws and maps change, always confirm the latest details with official state sources.
This article is part of our Civic Foundations series, which builds on how the US government works.
Key takeaways
- Gerrymandering is drawing district lines to advantage a party, group or incumbent, so the map can shape the outcome before votes are cast.
- Packing concentrates opposing voters into a few districts; cracking spreads them thin so they rarely win a majority.
- Both parties have used it. The pattern follows incentives and who controls the process, not one party’s character.
- The Supreme Court ruled in 2019 that federal courts will not decide partisan gerrymandering claims, though racial dilution claims and state-level challenges remain possible.
- Reforms include independent commissions, map-drawing criteria, state court review and ballot initiatives, each with trade-offs.
- Rules differ by state and change over time, so check official sources for your own district.
Frequently asked questions
What is gerrymandering in simple terms?
Gerrymandering is drawing the boundaries of voting districts to give one party, group or incumbent an advantage. Instead of voters choosing their representatives, the map can end up shaping which voters count most in each district.
Is gerrymandering illegal?
It depends on the type. Racial gerrymandering that dilutes minority voting power can violate the Constitution and the Voting Rights Act. In 2019, the Supreme Court ruled that federal courts cannot decide partisan gerrymandering claims, though some state courts and state constitutions do limit it. Check current rulings and your state’s rules.
Do both parties gerrymander?
Yes. Whichever party controls the map-drawing process in a state has historically been tempted to draw lines in its favor. Which party benefits in a given decade depends on who holds power in which states, not on one party being uniquely guilty.
Who draws congressional and legislative districts?
In most states, the state legislature draws the lines, often with the governor’s signature. Some states use independent or bipartisan commissions instead, and a few use hybrid systems. The rules vary by state and can change, so check your state’s official sources.
How often are district lines redrawn?
Typically once every ten years, after the national census counts the population. Courts can also order maps redrawn between censuses if they find a legal violation, and some states have redrawn mid-decade.