Gerrymandering Explained

What is gerrymandering?

Gerrymandering is drawing electoral district lines to give one party an unfair advantage. States redraw those lines after the census, and a gerrymandered map can help one side keep power even when more voters prefer the other party.

The term comes from Massachusetts Governor Elbridge Gerry, whose name was attached to a district shaped like a salamander in 1812. The practice is older than the name, but modern software makes it far easier to draw finely tuned partisan maps.

How Gerrymandering Works: Packing and Cracking

Two techniques, used together, can turn a 50-50 electorate into a 70-30 seat advantage.

Software like Maptitude processes precinct-level voter files, demographic projections, and multi-cycle election results. The output: maps that look reasonable but produce lopsided outcomes every cycle. You cannot tell a gerrymandered map by its shape.

How Gerrymandering Distorts Representation

In a fair system, a party that wins 50% of votes should win roughly 50% of seats. Gerrymandering breaks that relationship. In multiple states, the party with fewer votes holds the majority of seats.

Voters chose one party. Maps gave the seats to another.

Category	Value
Wisconsin 2012: Dems won votes, got 39% of seats	39%
Pennsylvania 2012: Dems won 51% of votes, got 28% of seats	28%
Texas 2025: GOP wins 53% of votes, could hold 80% of seats	20%

Percentage of seats won by the party that received the majority of statewide votes. A fair map would give ~50%. Source: Brennan Center.

In each case, the party that won the most votes received far fewer seats than their vote share warranted. The maps predetermined the outcome.

The efficiency gap: how many votes the map throws away

The efficiency gap measures how many votes a map wastes. A “wasted” vote is one that does not contribute to electing a representative: votes for losing candidates, and votes beyond what the winner needed. In a fair map, both parties waste roughly equal votes. In a gerrymandered map, one party’s voters are systematically wasted by the design of the districts. Above 7% is considered presumptively unconstitutional.

Four states had efficiency gaps above 12% — meaning the map structurally wasted more than 1 in 8 votes cast.

Four states wasted more than 1 in 8 votes through map design

Category	Value
Pennsylvania: 23.8% wasted	23.8%
Virginia: 22.3% wasted	22.3%
Wisconsin: 14.8% wasted	14.8%
North Carolina: 12.1% wasted	12.1%
Texas: 4.1% wasted	4.1%

Efficiency gap measures structurally wasted votes. Above 7% = presumptive unconstitutional. Source: University of Chicago Law.

The 16-seat structural advantage

“Partisan gerrymanders enabled politicians to entrench themselves in office as against voters’ preferences. And someplace along this road, ‘we the people’ become sovereign no longer.”

Justice Elena Kagan, dissent in Rucho v. Common Cause (2019)

Types of Gerrymandering

Partisan gerrymandering

Drawing maps so one party wins more seats than its vote share warrants. Both parties do it. Republicans have a larger structural advantage because they control more state legislatures.

Illinois Democrats: 14 of 17 seats (fair share: ~11). Texas Republicans: up to 80% of seats with 53% of votes.

Racial gerrymandering

Diluting minority voting power by packing or cracking communities of color. In South Carolina, the legislature moved 30,000 Black voters to a district 100 miles away. In Tennessee, the legislature carved Memphis — the state’s largest Black-majority city — into three Republican districts, eliminating the state’s only majority-Black congressional seat. The Voting Rights Act prohibited this, but the Supreme Court’s Callais ruling (2026) now requires proof of intentional discrimination, a standard that is nearly impossible to meet.

Prison gerrymandering

The Census counts prisoners where they are imprisoned, not where they lived. A rural district with a large prison gets more representation even though the prisoners cannot vote there. The community where those prisoners lived and will return to loses representation. 12 states have fixed this by counting prisoners at their home addresses, but 38 states still count them at the prison.

How the Courts Closed Every Avenue

Three Supreme Court decisions in seven years dismantled the legal framework for challenging gerrymandered maps. Rucho in 2019 closed federal courts. Alexander in 2024 let legislatures disguise racial targeting as partisan. Callais in 2026 rewrote the standard for proving discrimination.

1. 2019 Federal courts closed
2. 2024 Racial targeting called partisan
3. 2026 VRA standard rewritten

: 2019 — Federal courts closed (Rucho: partisan gerrymandering beyond judicial reach). 2024 — Racial targeting called partisan (Alexander: race-based sorting reframed). 2026 — VRA standard rewritten (Callais: must prove intentional discrimination).

Each ruling made the next challenge harder.

Legal remedies for gerrymandered maps

Period	Value
Before 2019	Federal + state courts
After 2026	State courts only (weakened)
Change	Three rulings in 7 years

Rucho v. Common Cause (2019)

5-4. Partisan gerrymandering declared a “political question” beyond federal courts. All challenges pushed to state courts. The majority acknowledged the maps were unfair but said courts cannot fix it.

Alexander v. South Carolina NAACP (2024)

6-3. South Carolina moved 30,000 Black voters to a district 100 miles away. The Court called it partisan, not racial. Legislatures can now target voters by race as long as they claim they targeted them by party.

Louisiana v. Callais (April 2026)

6-3. Louisiana’s two majority-Black districts ruled unconstitutional. Rewrote the 40-year Gingles framework, now requiring proof of intentional discrimination — a standard that is nearly impossible to meet.

“Today the majority straight-facedly holds that the Voting Rights Act must be brought low to make the world safe for partisan gerrymanders.”

Justice Elena Kagan, dissent in Louisiana v. Callais (2026)

Within days, Florida passed new maps. Tennessee eliminated its sole majority-Black district by carving Memphis into three Republican districts.

State courts: the last line

Alaska, Ohio, Utah, and Wisconsin courts struck down gerrymandered maps. But North Carolina’s court reversed itself after two Republican justices were elected. Ohio’s court struck down maps repeatedly; mapmakers refused to comply and used unconstitutional maps anyway.

State supreme court elections are low-turnout and high-impact. They determine whether gerrymandered maps survive.

The Most Active Mid-Decade Redistricting Since the 1800s

Net partisan shift: Republicans gained 7 seats, Democrats gained 6 (California). Net +1 Republican — but Virginia could add 4 more Democratic seats if enacted.

The Callais domino effect

Callais opened the door for every state with majority-minority districts to argue those districts are illegal. Tennessee moved within days. Alabama’s court-ordered second majority-Black district was vacated and remanded. Georgia Governor Kemp called a special session for June 17, 2026 to redraw all Georgia maps — though the new maps will take effect in 2028, not 2026.

The Supreme Court granted a 6-3 stay allowing Texas to use its new map in the 2026 election, despite a lower court ruling that it was an unconstitutional racial gerrymander. Virginia, Florida, Maryland, and Washington are all pursuing their own mid-decade redistricting. Only 43 of 435 House districts were rated competitive in 2024. Gerrymandering is making that number smaller by design.

Who Draws the Maps in Your State

In 29 states, the party in power draws the district lines that determine whether it stays in power. Only 8 states use independent commissions where no single party controls the outcome.

Independent commission

Advisory or backup commission

Nonpartisan process (Iowa)

Partisan legislature

Single at-large district

Sources: NCSL, Ballotpedia, Resist Now analysis

Who Draws Congressional Maps

State	Method	Detail
Alabama	Partisan legislature	Legislature draws congressional maps
Alaska	Independent commission	Redistricting Board appointed by governor, legislature, and chief justice
Arizona	Independent commission	Created by ballot measure (2000). Margins of victory 28% lower than national average.
Arkansas	Partisan legislature	Legislature draws congressional maps
California	Independent commission	Created by ballot measure (2008/2010). 5 Dem + 5 Rep + 4 no party. Produced 41% of national toss-up districts from 19% of all districts.
Colorado	Independent commission	Created by ballot measure (2018). 4 Dem + 4 Rep + 4 no party. 21 hearings, 5,000+ public comments.
Connecticut	Advisory/backup commission	Legislature draws congressional maps
Delaware	Single at-large district	Legislature draws congressional maps
District of Columbia	Single at-large district	Legislature draws congressional maps
Florida	Partisan legislature	Legislature draws congressional maps
Georgia	Partisan legislature	Legislature draws congressional maps
Hawaii	Advisory/backup commission	Legislature draws congressional maps
Idaho	Independent commission	Bipartisan commission. 3 appointed by each party.
Illinois	Advisory/backup commission	Backup commission if legislature deadlocks
Indiana	Partisan legislature	Legislature draws congressional maps
Iowa	Nonpartisan process	Nonpartisan legislative staff draw maps without political data. Legislature votes yes or no. Among the most competitive elections in the country.
Kansas	Partisan legislature	Legislature draws congressional maps
Kentucky	Partisan legislature	Legislature draws congressional maps
Louisiana	Partisan legislature	Legislature draws congressional maps
Maine	Advisory/backup commission	Legislature draws congressional maps
Maryland	Advisory/backup commission	Governor submits plan, legislature acts on it
Massachusetts	Partisan legislature	Legislature draws congressional maps
Michigan	Independent commission	Created by ballot measure (2018). 4 Dem + 4 Rep + 5 unaffiliated. Produced most competitive district in the nation.
Minnesota	Partisan legislature	Courts frequently intervene when legislature deadlocks
Mississippi	Advisory/backup commission	Backup commission
Missouri	Partisan legislature	Has bipartisan commission language but congressional maps drawn by legislature in practice
Montana	Independent commission	Districting and Apportionment Commission. Bipartisan with independent chair.
Nebraska	Partisan legislature	Legislature draws congressional maps
Nevada	Partisan legislature	Legislature draws congressional maps
New Hampshire	Partisan legislature	Legislature draws congressional maps
New Jersey	Advisory/backup commission	Bipartisan commission with tiebreaker
New Mexico	Partisan legislature	Legislature draws congressional maps
New York	Advisory/backup commission	Commission prepares maps, legislature has final authority
North Carolina	Partisan legislature	Among the most extreme gerrymanders. R+26 efficiency gap in 2024 map.
North Dakota	Partisan legislature	Legislature draws congressional maps
Ohio	Advisory/backup commission	Commission/backstop. Courts repeatedly rejected maps in 2022.
Oklahoma	Partisan legislature	Legislature draws congressional maps
Oregon	Partisan legislature	Legislature draws congressional maps
Pennsylvania	Advisory/backup commission	Legislative Reapportionment Commission for state maps. Congressional maps drawn by legislature.
Rhode Island	Partisan legislature	Legislature draws congressional maps
South Carolina	Partisan legislature	Legislature draws congressional maps
South Dakota	Single at-large district	Legislature draws congressional maps
Tennessee	Partisan legislature	Legislature draws congressional maps
Texas	Partisan legislature	Legislative Redistricting Board as backup if legislature fails
Utah	Advisory/backup commission	Independent commission created by ballot measure (2018), but legislature ignored its maps in 2021
Vermont	Single at-large district	Legislature draws congressional maps
Virginia	Advisory/backup commission	Created by constitutional amendment (2020) but commission deadlocked in 2021. Courts drew the maps. Commission structure remains.
Washington	Independent commission	Bipartisan commission. 2 appointed by each party + nonvoting chair.
West Virginia	Partisan legislature	Legislature draws congressional maps
Wisconsin	Partisan legislature	Among the most gerrymandered states. Governor used veto to force court-drawn maps in 2024.
Wyoming	Single at-large district	Legislature draws congressional maps

Independent commissions: Alaska, Arizona, California, Colorado, Idaho, Michigan, Montana, Washington.

Iowa’s model: A nonpartisan agency draws maps without political data. The legislature votes yes or no but cannot modify them. Iowa consistently produces among the most competitive elections in the country.

The other 29 states: The party in power draws the maps that determine whether it stays in power.

Why commissions work: partisan balance prevents domination

The most effective commissions share three design features: no single party gets a majority, cross-party votes are required to approve a map, and citizen commissioners replace politicians.

Independent commissions draw only 19% of all congressional districts but produced 41% of competitive toss-up races in 2024.

Share of toss-up districts from commissions

41%

Share of all districts drawn by commissions

19%

2.2x more competitive Brennan Center

Not all redistricting is gerrymandering

Redistricting is required. Gerrymandering is a choice. The difference matters for understanding what reform looks like.

• Redistricting after the census is required by law. Population shifts mean district lines must change. That process is neutral. Gerrymandering is when the process is weaponized for partisan advantage.
• Majority-minority districts are not inherently gerrymandering. Drawing districts to ensure minority communities can elect representatives of their choice was a core purpose of the Voting Rights Act. The Callais ruling made this harder, but the principle remains sound.
• Both parties gerrymander. Illinois Democrats drew maps giving themselves 14 of 17 seats. Maryland Democrats drew maps that eliminated a Republican district. The structural advantage is larger for Republicans because they control more state legislatures, but the practice is bipartisan.
• Competitive districts are not always possible. Natural geographic sorting (Democrats concentrated in cities, Republicans in rural areas) creates some noncompetitive districts without any manipulation. Gerrymandering makes it worse, but it is not the only cause.

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Frequently asked questions

Is gerrymandering legal? Partisan gerrymandering is effectively legal at the federal level since Rucho v. Common Cause (2019). The Supreme Court said federal courts cannot hear these claims. Racial gerrymandering is illegal under the 14th and 15th Amendments, but the Callais ruling (2026) made those claims much harder to win.

What are packing and cracking? The two techniques used to gerrymander. Packing concentrates opponents into a few districts where they win by huge margins. Cracking splits a community across districts so they cannot form a majority anywhere. Used together, they can turn a 50-50 electorate into a 70-30 seat advantage.

Do independent commissions work? Yes. Independent commissions draw only 19% of congressional districts but produced 41% of all toss-up districts in 2024 (Brennan Center). Arizona’s commission produced margins of victory 28% lower than the national average (University of Maryland). California’s commission made elections more competitive every year compared to the previous legislature-drawn maps (PPIC).

Can gerrymandering be fixed? Yes, through state-level reform. Ballot initiatives have created independent commissions in multiple states. State courts can strike down gerrymandered maps. And voters can elect state legislators and governors who support fair maps. See our redistricting explainer for the full process.

What is the efficiency gap? A mathematical measure of wasted votes: votes for losers plus votes beyond what is needed to win. An efficiency gap above 7% is considered presumptively unconstitutional. Pennsylvania’s 2012 map had an efficiency gap of 23.8%.

What you can do

1. Support independent redistricting commissions in your state. Ballot initiatives created them in Arizona, California, Colorado, Michigan, and Virginia. If your state is one of the 29 where the legislature draws its own maps, push for a commission. Campaign Legal Center and Common Cause provide model legislation. Use the letter and call script below.

2. Vote in state supreme court elections. After Rucho, state courts are the only venue for partisan gerrymandering claims. These races are low-turnout and high-impact. They determine whether gerrymandered maps survive.

3. Support redistricting litigation. Campaign Legal Center, NAACP Legal Defense Fund, and Brennan Center litigate redistricting cases.

4. Know who draws your maps. If your state legislature draws districts, your state legislators are the most important people in determining whether your congressional vote counts. Vote for state legislators who support independent commissions.