Princeton Gerrymandering Project

Update - Dec. 22, 2020

A few decades ago, legislators used paper maps, calculators, and pens to draw district lines. Today, redistricting is done with high-tech hardware, software, databases, and professional programs. In this update, the Princeton Gerrymandering Project wanted to feature a few of the key technological tools available to the public, in anticipation of the 2021 redistricting process.


OpenPrecincts: OpenPrecincts aims to be an open-source database of precinct-level shapefiles for all 50 states, the District of Columbia, and Puerto Rico matched with current and historical election results. Precinct information and historical election results are crucial--a close reading of such data can provide a better understanding of how people vote, and how districting plans impact political representation.

In 2021, state governments will draw new congressional and state legislative districts. Some states will draw fair districts; others will inevitably produce gerrymanders. The OpenPrecincts database provides analysts and activists with the necessary information to understand new maps before they take effect.

OpenPrecincts is also compatible with several open-source redistricting programs that allow users to draw plans of their own. As a tool, OpenPrecincts makes the redistricting process accessible to all citizens, and helps ensure that the next decade’s districts are fair and representative. OpenPrecincts often runs on OpenElections data. OpenElections is an effort to gather-precinct level election data as quickly after big elections as possible. 

OpenPrecincts is available to anyone, regardless of political leaning or technical background. All interested voters and members of the public can go to to learn more about the project.

Representable: Federal law allows redistricters to honor “communities of interest.” A community of interest is best defined as groups of people who share similar interests, and who may be affected in special ways by legislation. These interests can be racial, ethnic, religious, social, cultural, or economic. Across the nation, more than 20 states explicitly consider communities of interest when drawing state legislative districts, congressional districts, or both. Representable is a free, online service that allows the public to draw communities of interest, so that mapmakers are forced to keep these communities intact. The process of drawing and documenting communities of interest with Representable is likely to prove a powerful tool for fighting gerrymandering in 2021.

Representable is now available for all 50 states and the District of Columbia. Organizations can reach out to Representable about launching a community-mapping drive in their state!

Mapmaking Software: Today, there are a number of tools citizens can access to draw district plans. DistrictR, District Builder, and Dave’s Redistricting are free online platforms the public can use to craft, analyze, and share electoral maps.  Another line-drawing option is “My Districting” by CitygateGIS. CitygateGIS provides services in the areas of redistricting plan creation, public meetings, analysis, and enhanced report production. For a moderate fee, voters and advocates can also use Maptitude or Esri

PlanScore: This site scores historical districting plans and provides tools to score new maps. In particular PlanScore uses the efficiency gap, partisan bias, and the mean-median difference to measure partisan gerrymandering. As a redistricting resource, the creators have used these metrics to score state legislative and congressional district plans, including maps that date back to 1972. PlanScore offers scoring services; interested parties can upload a map to instantly receive information about partisan fairness. This is useful when comparing multiple maps in the same state.

PGP site

Princeton Gerrymandering Website: The Princeton Gerrymandering Project website is a hub of redistricting information and resources. Our interactive map provides an overview of the redistricting process in each state, and the best pathways to reform. Analysts and computer scientists can use our site to access the data and code we use to score maps and test plans for partisan fairness. Finally, PGP is constantly writing new policy papers and legal articles. Friends of reform can navigate to our scholarly works section to read more about our studies and submitted publications.

In summary, there are a number of powerful tools to help get advocates and voters more involved with the upcoming redistricting cycle. The Project looks forward to working with the public to help ensure fair districts in 2021.

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