Voter SuppressionGerrymandering

What is Gerrymandering?

03.03.2022 Public Wise Research


The history of redistricting, the process by which districts are drawn for federal and state office, begins in 1810. Elbridge Gerry, the governor of Massachusetts from 1810 to 1812 and an original signer of the Declaration of Independence, approved a Massachusetts state senate map that was drawn to benefit Republicans. The map produced the district shown below, which people observed resembled a salamander, or in this case a “Gerrymander.” The rest, as they say, is history. The practice of gerrymandering, or manipulating district lines to advantage (or often disadvantage) a particular party or community of individuals has been a feature of redistricting for over 200 years.

“The Gerrymander: A New Species of Monster” Boston Gazette, March 26, 1812. (Library of Congress)


Reapportionment v. Redistricting

To understand the types, causes, and impacts of gerrymandering, it is important to have a good grasp on reapportionment, redistricting, and how the two practices relate to each other. Reapportionment, like redistricting, occurs every 10 years and relies on data acquired by the US Census. Reapportionment is concerned with the number of representatives allotted to each state in the House of Representatives, according to population size. For example, during the most recent reapportionment in 2020 seven states lost one seat, five states gained one seat, and one state gained two seats. Ultimately, however, the number of total seats in the House of Representatives remains constant. Importantly, reapportionment occurs at the federal level. 

Redistricting, on the other hand, occurs at the state level and is concerned with how representation is spread across the state. The process is a cinch for states with relatively smaller populations, such as Wyoming, which receives a single congressional district that covers the entire state. But in more populous states, such as Texas, the state has to determine how its given number of representatives will be distributed (both geographically and by population). Today, states are divided into congressional districts, where the residents of those districts each elect their own representative. Redistricting occurs after reapportionment and also uses the most recent census data. 

Redistricting prior to Baker v. Carr

Throughout the 1800s and for much of the 1900s, reapportionment and redistricting looked very different compared to today. First, for the majority of that time period, the size of Congress grew as the US population grew. This meant that allocation of representatives was not a zero-sum game, with one state losing seats if another state gained seats. This ended in 1929 when Congress passed the Permanent Apportionment Act, which limited the number of seats in the House of Representatives. Second, there was not a clear set of guidelines for the creation of districts. For example, one of the early problems with redistricting was that many states were not redistricting regularly and when they were, they often drew districts with large population disparities. The effect of this was that the vote of an individual in a district with a small population was inherently more valuable than the vote of an individual in a district with a larger population. 

Because of this inequality, in 1946 an Illinois resident filed a lawsuit against Illinois officials claiming that congressional districts in the state lacked compactness of territory and approximate equality of population and thus were in violation of the US Constitution and the Reapportionment Act of 1911. The case, Colegrove v. Green, made it all the way to the Supreme Court, which ultimately upheld the decision of the lower court to dismiss the complaint. Justice Frankfurter wrote in his opinion that the issue of fair representation in the House of Representatives is left to Congress and that it would be unwise for the court to make a decision regarding Illinois’s map and enter this “political thicket.” 

One Person, One Vote and Baker v. Carr

Justice Frankfurter’s “political thicket” proved to be important in the history of Supreme Court decisions on redistricting and gerrymandering. Quite simply, litigating gerrymandering boils down to whether the Supreme Court has the power to intervene when legislative maps are “unfair.” The answer: Sometimes. 

Nearly 20 years later in 1962, the Supreme Court ruled on another redistricting case, Baker v. Carr. In Baker, the court ruled that redistricting is not in fact a political question and thus is a justiciable issue (i.e. an issue the Supreme Court can weigh in on). Baker had a domino effect just a few years later in Supreme Court cases Wesberry v. Sanders and Reynolds v. Sims. The opinions in these two cases established a requirement for federal and state legislative districts to be of approximately equal size, adhering to the principle of one person, one vote. 

How Does One Gerrymander? 

Post Baker v. Carr, states now had certain guidelines as to how they must draw legislative maps. Most importantly, they could not dilute or increase the voting power of a given community by manipulating the population size of the district. But, as we have learned over the years, there are other ways to control representation through districting. Specifically, classic gerrymandering practices such as cracking, packing, and stacking were employed. Charles S. Bullock discusses these three methods of gerrymandering at length, particularly as it pertains to how they have been used following the passage of the Voting Rights Act to disadvantage Black voters. 

  • Cracking – Cracking is a practice by which a community or voting bloc is divided up, or “cracked,” into multiple districts to dilute its power and voice. For example, if a given community is large enough to constitute a majority and win a congressional seat, it might be split into three separate districts to divide the vote, making smaller minority voting blocs and ensuring the group does not receive representation. 
  • Packing – Packing, the sibling of cracking, is when a community is intentionally crammed into a given district in order to contain its voice and power. For example, if a given community is large enough to constitute a majority interest in multiple districts, the community might be pushed into a single district to concentrate and thus limit the voting power of the group. 
  • Stacking – Stacking occurs when a majority community is grouped with multiple other different majority communities, thus making it a minority interest in the larger group. This historically occurred in areas in the South where majority Black single member districts were combined with multiple majority white single member districts to produce a large majority white multi member district. This practice ensures that what might have been a 3-1 ratio of representation becomes 4-0. 

This New York Times article provides a lot of great information on redistricting and in particular it provides visuals for packed and cracked districts (see numbers 12 and 13). 

How Can We Tell Gerrymandering Has Occurred? 

Now that we have discussed different methods of gerrymandering, we can discuss how exactly one can tell if a district map has been gerrymandered. 

Relatively recently, a new method of evaluating how gerrymandered a given legislative map is was developed. This method, created by Nicholas Stephanopoulos and Eric McGhee of the University of Chicago, looks at the “efficiency gap” of a map. This efficiency gap is determined by calculating the votes that are wasted in a given election. A wasted vote is any vote cast for a losing candidate in a district or any vote cast for a winning candidate over the number of votes they needed to win. This term “wasted” is used because these votes do not directly contribute to the election of a representative.  

The efficiency gap, in addition to being a relatively simple calculation, also lends itself to the establishment of thresholds above which a legislative map could be declared unconstitutional. Stephanopoulos and McGhee propose a two seat margin for congressional maps and an efficiency gap of eight percent for state legislature maps. 

This framework is very useful, as it focuses on voter impact rather than hypothetical election outcomes. But it still has problems, many of which are outlined in this piece by the New York Times. Most notably, the efficiency gap does not take into account the unavoidable “packing” and “cracking” that can occur due to geography. For example, Democratic voters are often naturally packed into cities where a Democratic candidate may win an election with a very large majority of the vote. In these situations, there is a high percentage of wasted votes, but no malicious gerrymandering has technically occurred. 

Another way to assess a gerrymandered district is to look at the partisan bias. Assessing partisan bias was part of the argument made in the 2018 Supreme Court case Rucho v. Common Cause. The partisan bias of a map was calculated by determining the number of seats a given party would win if they had won an average of 50% of the vote

There are many more metrics and methods that can be used. For example, you can also look at partisan gerrymandering using a Monte Carlo simulation with an ensemble of redistricting maps. If anything, the multitude of methods should demonstrate just how complicated quantifying gerrymandering can be.  

Is gerrymandering illegal? 

While gerrymandering has been occurring for centuries, in the past decade alone the Supreme Court has heard cases that address both partisan and racial gerrymandering. 

Gill v. Whitford, heard by the Supreme Court in 2017, was a case regarding what the plaintiffs argued was a partisan gerrymander in Wisconsin designed to dilute the voting power of Democrats. In a unanimous decision, Chief Justice John Roberts wrote in the opinion that the plaintiff did not have standing, meaning that the Supreme Court was not the proper venue for the case to be heard, effectively punting on the Court’s ability to rule on partisan gerrymanders. 

Cooper v. Harris, heard by the Supreme Court in 2016, addressed racial gerrymandering. The plaintiffs argued that following the 2010 census, North Carolina had drawn its maps to pack Black voters in two specific districts to reduce their voting power in other districts. The Supreme Court found in agreement with the lower court that North Carolina’s districting plan was a racial gerrymander. Importantly, the Court found that “a State may not use race as the predominant factor in drawing district lines unless it has a compelling reason.”

The most obvious place to remedy gerrymandering is, according to the Supreme Court, the legislature, but it is an issue that continues to be litigated across the country. 

Who is doing this? 

Both parties are guilty of using gerrymandering to manufacture a political advantage. In the next part of this series we will discuss the most recent set of redistricting maps and which states have gerrymandered maps in favor of a particular party or group. However, an examination of past redistricting plans reveals that in recent history, Republicans in particular have used redistricting as a tool for creating a significant partisan advantage in the House of Representatives and state legislatures. 

A report on extreme maps authored by the Brennan Center for Justice revealed that 2011 redistricting produced maps that were consistently biased towards Republicans. In the 26 states that account for 85% of congressional seats, Republicans saw an advantage of 16-17 seats as a result of redistricting bias. 7 states (Michigan, North Carolina, Pennsylvania, Florida, Ohio, Texas, and Virginia) account for the majority of the bias. According to the report, when Democrats have sole control of the redistricting process they too gerrymander maps to their advantage. That being said, the advantage to Democrats impacts a relatively smaller portion of districts, reducing the overall partisan bias. 


Gerrymandering has been a staple of American democracy since nearly the country’s founding. Most recently, Republicans have used party control of the redistricting process to create huge partisan advantages in Congressional maps and, in certain cases, dilute the power of Black voters. While Republicans are by no means the only party guilty of gerrymandering, their use of packing and cracking in recent decades has had an undeniable impact on the makeup of Congress and racial and partisan gerrymandering cases have been and continue to be litigated across the country. The rest of this series will address gerrymandering in 2021, long-term effects of gerrymandering, and potential solutions to this problem.