Gerrymandering Explained
The maps that decide elections before a single vote is cast. How district lines get drawn, who draws them, and why your vote may count for less than you think.
97%
House incumbents who win re-election in gerrymandered districts
59M
Americans in districts rated "uncompetitive" after 2020 redistricting
2011
Year Republicans launched REDMAP, the coordinated gerrymandering strategy
0
Federal courts that can strike down partisan gerrymandering (since Rucho v. Common Cause, 2019)
What Gerrymandering Is, and Where It Came From
The name itself is a piece of American political folklore. In 1812, Massachusetts Governor Elbridge Gerry signed a bill redrawing state senate districts to benefit his party. One district, snaking through Essex County, was drawn in such a contorted shape that a newspaper cartoonist compared it to a salamander, and dubbed it a “Gerrymander.”
There are two core techniques, and they work in tandem. Packing means concentrating opposition voters into as few districts as possible. They win those districts by enormous margins, but those surplus votes are wasted. Cracking is the complement: splitting opposition voters across multiple districts so they’re never a majority in any of them. Together, packing and cracking let a mapmaker predetermine outcomes before a single ballot is cast.
The math is counterintuitive until you see it. Imagine 60 voters across a 6-district grid: 36 favor Party A (60%), 24 favor Party B (40%). With fairly drawn districts: 4 seats for A, 2 for B. With cracking and packing: a skilled mapmaker can hand Party B all six seats despite losing the popular vote by 20 points. Democracy on paper; minority rule in practice.
Both parties have done this. But the scale, precision, and coordination of the practice has varied dramatically across eras, states, and parties, as has the technology available to those doing the drawing.
Technique 1
Packing
Concentrating opposition voters into a small number of districts. They win those seats by landslide margins of 80%+, but every vote above 50% is wasted. It doesn’t elect a second representative.
Result
Fewer total seats despite high vote totals in packed districts.
Technique 2
Cracking
Splitting opposition voters across many districts so they form a permanent minority in each one. Thirty percent here, thirty percent there, never enough to win anywhere.
Result
Zero representation despite significant overall vote share.
Who Draws the Lines, and How
The U.S. Constitution requires a census every ten years. After each one, district lines are redrawn to account for population shifts. In most states, the legislature that happens to be in power at that moment draws both congressional and state legislative maps. The party that controls the statehouse draws the lines for elections it will compete in. The conflict of interest is not incidental. It is the system.
The timeline matters enormously. The 2020 census data was released in 2021. States spent 2021 and 2022 drawing new maps. Those maps govern every election from 2022 through 2030, covering six congressional elections and ten state legislative cycles, all determined by whoever happened to control state government in the winter of 2021.
This is why state legislative elections in years ending in 0 are called the “hidden elections.” A $50 million investment in state races in a census year can be worth billions in structural political advantage over ten years.
State Legislature
Most states. Both chambers vote; governor can sign or veto. The dominant model, and most susceptible to partisan manipulation.
Independent Commission
15 states including CA, AZ, and MI. Appointed body, not legislators. Varying degrees of true independence depending on appointment process.
Bipartisan Commission
A few states. Requires cross-party agreement to adopt any map, which tends to produce more moderate outcomes, or stalemate.
Courts (Last Resort)
Federal or state courts draw maps when legislatures deadlock, miss deadlines, or when existing maps are struck down by judicial order.
Case Study
The REDMAP Strategy
In 2010, the Republican State Leadership Committee launched REDMAP, the Redistricting Majority Project. The strategy: invest heavily in state legislative races in 2010 (a census year), win control of state governments, and draw favorable maps for the following decade.
Cost: ~$30 million. Result: Republicans won 700+ state legislative seats and took control of redistricting in Pennsylvania, Ohio, Michigan, and North Carolina, securing structural advantages that persisted for a decade regardless of how national vote totals shifted.
$30M
Invested in state races
700+
State legislative seats flipped
10 yrs
Of map control secured
The Precision Gerrymander: How Technology Changed Everything
For most of American history, gerrymandering was a blunt instrument. Mapmakers worked from rough census tallies and political intuition, hand-drawing districts on paper. In the 1990s, GIS software changed the calculus. The real revolution came in 2010. By then, mapmakers had access to tools of a fundamentally different character:
- Voter file data: Party registration and complete voting history for every registered voter in the state, down to individual precincts and often individual households.
- Consumer data: Purchasing patterns, magazine subscriptions, TV viewing habits correlated with political behavior, with dozens of commercial data points mapped to partisan affiliation.
- Precinct-level results: Exact vote margins in every precinct across multiple election cycles, allowing mapmakers to model how any district configuration would have performed historically.
- Simulation software: The ability to generate and evaluate thousands of district configurations in minutes, selecting the one with the optimal partisan outcome while satisfying legal requirements.
Pennsylvania’s 2011 congressional map, struck down by the state supreme court in 2018, was so precisely drawn that Democrats needed to win the statewide popular vote by roughly ten points just to win half the congressional seats. That isn’t bad luck. That’s engineering.
Pre-1990
Hand-Drawn Maps
Rough census data, paper maps, political instinct. Gerrymandered by intent but limited by tools. Imprecision was common.
1990–2010
GIS Software Era
Geographic information systems allowed demographic overlays and systematic testing. Partisan advantage became more reliable and more defensible in court.
2010–Present
Surgical Precision
Full voter files, consumer data, simulation software running thousands of configurations. Maps drawn to statistical implausibility of natural occurrence.
Race, the Voting Rights Act, and the Courts
For decades after the Civil Rights era, the most powerful check on gerrymandering was the Voting Rights Act of 1965. Section 5 required states with histories of racial discrimination to obtain federal “preclearance” before implementing any changes to voting maps. In 2013, Shelby County v. Holder gutted the preclearance formula. Section 5 enforcement effectively ended.
Racial gerrymandering, which uses race as the predominant factor in drawing district lines, is still unconstitutional under the Equal Protection Clause. Shaw v. Reno (1993) established that districts cannot be so irregularly shaped that race is the only plausible explanation. But the VRA’s Section 2 also requires states to create majority-minority districts when populations are sufficiently large and concentrated. The law simultaneously prohibits and sometimes mandates considering race. Courts have spent three decades navigating that tension.
In 2023, Allen v. Milligan produced one of the few recent bright spots. Alabama had drawn a map with one majority-Black district out of seven, despite Black residents comprising 27% of the state’s population. The Supreme Court, 5–4, ruled that the map violated Section 2 by diluting Black voting power. The state was ordered to draw a second majority-Black district.
Federal courts cannot strike down maps for partisan gerrymandering. Rucho v. Common Cause (2019) closed that door. Courts can strike down racial gerrymanders. This creates a direct incentive for mapmakers to use race as a proxy for partisanship, then claim in court that the motive was partisan, not racial.
1993
Shaw v. Reno
Established that racial gerrymandering can violate Equal Protection even when creating majority-minority districts. Districts cannot be “so bizarre on their face” that race is the only explanation.
2019
Rucho v. Common Cause
Federal courts have no jurisdiction over partisan gerrymandering claims, a “political question” beyond judicial reach. State courts remain an avenue.
2023
Allen v. Milligan
Alabama’s map diluted Black voting power in violation of VRA Section 2. The 5–4 ruling ordered a second majority-Black district, one of the few recent VRA victories.
Reform: What’s Been Tried and What Works
Independent Redistricting Commissions
- 15 states use some form of independent or bipartisan commission to draw district lines.
- California (2008) and Michigan (2018) created citizen commissions via ballot initiative, with members selected through an application process, not the legislature.
- Arizona State Legislature v. Arizona IRC (2015) confirmed that ballot initiatives can remove redistricting authority from legislatures entirely.
- Evidence: states with independent commissions produce more competitive districts on average, though commissions are not immune to manipulation.
Algorithmic and Mathematical Approaches
- “Shortest split-line” method: a purely mathematical algorithm that draws districts by repeatedly splitting states with the shortest possible line. Nonpartisan, but ignores communities of interest.
- Ranked-choice voting as a partial solution: multi-member RCV districts make gerrymandering much harder since winning requires capturing multiple seats in the same geography.
- The efficiency gap and other metrics: scholars have proposed legal standards courts could apply if Rucho is ever revisited.
State Courts as the Remaining Venue
- After Rucho closed federal courts to partisan gerrymandering claims, state courts became the primary battleground.
- The Pennsylvania Supreme Court struck down the 2011 map under the state constitution’s free and equal elections clause (2018), and drew a replacement map itself.
- North Carolina’s Supreme Court has shifted positions multiple times as control of the court changed between parties.
- Key insight: state court outcomes on gerrymandering are heavily influenced by the partisan composition of the court, which is itself determined by elections.
Independent Commission
- +Removes mapmaking from legislators
- +Harder to manipulate with robust application process
- –Depends heavily on how commissioners are selected
Multi-Member RCV Districts
- +Makes packing and cracking much harder
- +Already used in some state legislatures
- –Requires fundamental change to election structure
Algorithmic Drawing
- +Purely mathematical; eliminates intentional manipulation
- –Ignores communities of interest
- –Produces mathematically neutral but visually bizarre maps
State Courts
- +Available now without new legislation
- +Can produce fast results
- –Vulnerable to court composition changing
- –Not durable without constitutional amendment
What Gerrymandering Actually Does to Democracy
Pennsylvania 2012
Democrats won 83,000 more votes statewide, but Republicans won 13 of 18 congressional seats.
Wisconsin 2012
Democrats won the majority of votes statewide, but Republicans won 60 of 99 state assembly seats.
These results are mathematically close to impossible under fair maps. They are not anomalies They are designed outcomes.
Reduced Competition = Reduced Accountability
Safe seats reduce electoral accountability. Incumbents fear primary challengers more than general election opponents, which pushes behavior toward the base, not the median voter. Research shows representatives from competitive districts have more moderate voting records and greater constituent responsiveness.
The Nationalization Effect
Gerrymandering makes local elections function as proxies for national party contests. Voters in heavily gerrymandered states have fewer competitive races to anchor attention; the national party brand becomes the dominant frame.
Voter Disengagement
Research shows voters in uncompetitive districts are less likely to vote, less likely to contact representatives, and report lower political efficacy. “Why vote if the outcome is predetermined?” is a rational response to a structurally rigged map.
Gerrymandering doesn’t just pick winners. It picks the voters. By choosing which communities end up in which districts, mapmakers decide whose voices get amplified and whose get wasted. The result is a legislature that can remain structurally unresponsive to majority opinion for an entire decade.
What You Can Do
The next redistricting cycle begins after the 2030 census. That gives nearly a decade to change state laws before it matters, but only if the organizing starts now.
Dave’s Redistricting App
davesredistricting.org
Draw your own districts. The most powerful tool for understanding how lines shape outcomes. Lets you draw and analyze maps at the precinct level with partisan performance data built in.
Ballotpedia Redistricting Tracker
ballotpedia.org
Tracks redistricting activity in all 50 states, court cases, timelines, and current maps. The best single source for following the legal landscape across the country.
State-Level Advocacy
Common Cause · League of Women Voters
Redistricting reform requires winning state legislature races or ballot initiative campaigns. Common Cause and the League of Women Voters run active state-based campaigns.
2030 Census Participation
census.gov
Accurate census data is the foundation of redistricting. Undercounts in minority communities directly affect political representation. Ensure your household and neighbors are counted.
Resources
- 01redistricting.lls.edu: All About Redistricting: the most comprehensive academic resource on redistricting law.
- 02planscore.org: PlanScore: grades district maps for partisan fairness using multiple metrics.
- 03gerrymander.princeton.edu: Princeton Gerrymandering Project: grades every state’s maps A through F.
- 04davesredistricting.org: Dave’s Redistricting App: an interactive mapping tool for the public.
- 05commoncause.org: Common Cause: redistricting reform advocacy across all 50 states.
- 06lwv.org: League of Women Voters: runs state-level campaigns for independent commissions.