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What Is Gerrymandering? How District Lines Can Shape Elections

Gerrymandering is the strategic drawing of voting districts to favor a political outcome. It can change how votes translate into seats through tactics known as cracking and packing.

Daniel Okafor

By Daniel Okafor · Business Editor

4 min read

Gerrymandering is the strategic manipulation of voting-district boundaries to favor a political outcome, usually based on partisanship or race. According to the Campaign Legal Center and the Bipartisan Policy Center, it can give a party, incumbents, or particular racial groups an electoral advantage.

The stakes are representation: district lines determine which voters are grouped together to elect officials. The Brennan Center for Justice and a 2023 research paper say map design can affect how votes translate into seats, including by reducing electoral competition and making a legislature less responsive to changes in voter preferences.

Gerrymandering versus redistricting

Redistricting is the routine process of redrawing electoral-district boundaries. The Bipartisan Policy Center says states generally redraw congressional and state legislative districts after the decennial census, using population data after House seats are apportioned among the states.

According to the Campaign Legal Center, districts within a state are intended to have roughly equal populations under the “one person, one vote” principle. Redistricting also occurs for local bodies, including city councils, county boards, and school boards.

Redistricting rules and map-drawing authority vary by state, the Bipartisan Policy Center says. Common criteria include contiguous districts, compactness, preserving political subdivisions, and keeping communities of interest together.

How cracking and packing work

The Brennan Center identifies cracking and packing as two basic techniques. Map drawers can use both in the same plan.

  • Cracking splits a targeted group across several districts. With too few supporters in each district, the group may be unable to elect its preferred candidate in any of them.
  • Packing concentrates a targeted group in a small number of districts. The group may win those seats by overwhelming margins while having less influence in surrounding districts.

A simplified example

Imagine five districts with 20 voters each and 40 voters statewide who support Party A. If eight Party A supporters are placed in each district, Party A is a minority in all five districts. This illustrates the basic logic of cracking.

If the 40 Party A supporters are instead concentrated in two districts, Party A could win those two seats while Party B wins the other three. Real maps face geographic and legal constraints, but the example shows why the placement of voters can affect seat outcomes.

Partisan, racial, and incumbent-protection maps

The Bipartisan Policy Center describes partisan gerrymandering as drawing boundaries to increase a party’s chances of electoral success. It also identifies incumbent-protection gerrymanders, in which both parties may draw maps that protect current officeholders.

According to the Campaign Legal Center, racial gerrymandering involves sorting voters with race as a predominant focus. The organization separately describes racial vote dilution as district arrangements that reduce the electoral power of voters of color.

Why a district’s shape is not enough

An irregular outline does not by itself prove gerrymandering. The Brennan Center says districts can follow geographic features, municipal boundaries, or communities with shared representational needs; a map drawn for partisan advantage can also appear compact and regular.

A gap between a party’s vote share and seat share is also not enough on its own. The 2023 research paper says voter geography, winner-take-all districts, and state redistricting rules can all affect seat outcomes.

Researchers can compare an enacted map with simulated alternatives that use the same geographic units and state-specific requirements, according to the paper. That approach can help distinguish effects of line drawing from effects of geography and legal constraints; evidence of intent may also be needed in litigation.

What the law says

The Bipartisan Policy Center says the Supreme Court held in Rucho v. Common Cause in 2019 that partisan-gerrymandering claims are political questions beyond the reach of federal courts. State constitutions and laws can still restrict partisan gerrymandering, and state courts have invalidated maps under state rules.

Federal law separately restricts racial discrimination in voting and districting, including through the Voting Rights Act, according to the Bipartisan Policy Center.

Where the term came from

The Campaign Legal Center traces the term to 1812, when Massachusetts Gov. Elbridge Gerry approved a state Senate map that benefited his Democratic-Republican Party. The Boston Gazette published a “Gerry-mander” cartoon after critics said one district resembled a salamander.

Frequently asked questions

How do cracking and packing work in gerrymandering?

Cracking splits a targeted group across several districts so it may be too small to elect its preferred candidate in any one district. Packing concentrates the group in a few districts, where it may win by large margins but have less influence elsewhere. The Brennan Center says both techniques can be used in the same map.

Is every oddly shaped voting district gerrymandered?

No. The Brennan Center says a district may be irregular because it follows geographic features, municipal boundaries, or a community of interest. It also says a map designed for partisan advantage can look compact and regular.

Is partisan gerrymandering illegal in the United States?

The Bipartisan Policy Center says the Supreme Court ruled in Rucho v. Common Cause that partisan-gerrymandering claims are beyond the reach of federal courts. State laws and constitutions can still prohibit the practice, and state courts can review maps under those rules.

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