Lesson originally published Sept. 28, 2016 and updated Oct. 19, 2025. See transcript here. The image in the video is an example of gerrymandering in Maryland’s 3rd congressional district.

1. After the U.S. Census every 10 years, state legislatures are responsible for redrawing electoral districts to reflect population changes. Because state legislatures are partisan bodies, those electoral districts are frequently drawn with the interest of the state legislature’s majority party in mind. This partisan redistricting is known as “gerrymandering” after Massachusetts Governor Elbridge Gerry, who approved a salamander-shaped electoral district that benefited his party in 1812.
2. Most states have some rules for redrawing district lines, and the most common guideline is contiguity. In other words, one must be able to travel to any part of the district without crossing district lines. However, fewer states have compactness guidelines, so districts are often jagged and irregularly shaped. Some of the most irregular districts include the “praying mantis” of Maryland’s third congressional district, the “earmuffs” of Illinois’s fourth congressional district, and “Goofy kicking Donald Duck,” or Pennsylvania’s seventh congressional district.
3. Gerrymandering is used to give the majority party the greatest number of districts that they can reasonably win and the minority party the fewest number of safe districts.
4. Two techniques are often used for partisan gerrymanders: “packing” and “cracking.” Packing involves concentrating as many voters from the minority party as possible in one district so their ability to swing surrounding districts is inhibited. Cracking involves spreading voters from the minority party across many districts so that they are unable to attain a majority.
5. Both Democrats and Republicans have utilized gerrymandering to their advantage. However, because the GOP has had a sizable advantage in statehouses and governors countrywide since the 2010 Census, many congressional and legislative districts were redrawn in their favor. As a result, Democrats won a plurality of the Congressional vote in 2012 but failed to take control of the House of Representatives.
6. The severity of gerrymandering is evaluated in an approach developed by two University of Chicago professors called an efficiency gap. Votes above a candidate’s threshold to win in a packed district are considered surplus votes and votes for a candidate that cannot win in a cracked district are considered lost votes. Lost votes and surplus votes are summed to determine the number of wasted votes. The efficiency gap is the difference in wasted votes between the two parties divided by the total number of votes cast.
7. The courts have struck down maps in multiple states that weaken the electoral power of minorities, including in Texas. The Supreme Court has never intervened because of unfair partisan advantage.
8. However, in November 2016, a federal court struck down Wisconsin’s district map as unconstitutional because it unfairly minimized the influence of Democratic voters. On June 19, 2017, the Supreme Court agreed to hear the case, Gill v. Whitford .
9. In the 1986 case of Davis v. Bandemer, the Supreme court ruled that if legislatures draw districts based on party lines, they could, in theory, be in violation of the Constitution. However, the Court remained divided on what qualified as unfair. Gill v. Whitford could figure out if there is a way to determine whether or not partisan gerrymandering goes too far.

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