Changes underway in Congressional redistricting

Colorado released its first draft of a new map of Congressional districts. We explain its new process and look at other states following the same path. Lawyers from the Princeton Gerrymandering Project and Brennan Center's Democracy Project give us their perspective.

Senate redistricting chair vows to redeem process as he plans to limit public’s input

Miami Herald, September 2021 Another non-partisan group, RepresentUS, has teamed up with the Princeton Gerrymandering Project to create the Redistricting Report Card, an algorithm that identifies gerrymandering as it happens and gives states grades on proposed voting maps.

You (Yes, You!) Can Help Texas Legislators Draw New District Maps

“I mean, I think it’s a little cliché at this point, perhaps, but redistricting is the process by which… legislators are picking their constituents rather than the other way around,” he said. “Which then obviously skews the way the laws are written and the way that laws are passed because if communities are unfairly represented, nobody’s really listening to their voices.” In Texas, public input is allowed. So could average citizens do a better job of drawing these maps? Podowitz-Thomas says citizens with the right tools can.

Let Math Save Our Democracy

The New York Times (2015)

The Great Gerrymander of 2012

The New York Times (2013)

Remapping 2021 | A wake-up call for Colorado’s redistricting commissioners as deadlines loom

Colorado Sun, September 20, 2021 All three of Colorado’s staff-drawn congressional map proposals earned an “A” for partisan fairness, based on an analysis released Thursday by the Princeton Gerrymandering Project, a nonpartisan group aimed at eliminating gerrymandering. All three Colorado congressional draft maps, however, received a “C” — an average grade — for political competitiveness and geographic features, such as compactness and the number of counties that are divided. 

Election-Map Challenges to Test Fine Line Between Race, Politics

Bloomberg Law, August 18, 2021 But those cases “may not move fast enough” to prevent 2022 elections “under maps that are packing minority voters,” said Adam Podowitz-Thomas, senior legal strategist for the Princeton Gerrymandering Project and the Princeton Electoral Innovation Lab.

Slaying the Partisan Gerrymander

The American Prospect (2017)

Census delay sends redistricting ripples nationwide

Jason Rhode and Sandra Chen are quoted.

Centrist Democrats’ Departures Challenge Party’s Control of House

Some experts say the potential GOP advantage may be overstated because Democrats control the process in a number of states that are losing seats. “They have the latitude toredraw and potentially to eliminate a Republican district,” Samuel Wang, who runs the Princeton Gerrymandering Project, said about Illinois.

Census data release will start House redistricting scramble

Roll Call, August 2021 “There is a nontransparent process … done behind closed doors, and that leads to gerrymandering, leads to the building of districts where there is no competition, and where an individual or an entire party or other group may gain an advantage,” said Sam Wang, director of the Princeton Gerrymandering Project. “We’ve been operating on a different track, and this new track is really something that’s come up in the last five years or so. It’s the possibility that citizens and reform groups can talk back.”

MapLab: Citizen Mappers Fight for Fair Districts

Bloomberg Citylab MapLab, August 11, 2021 mentioned

Opinion: The GOP strategy for retaking power is about to take an ugly new turn

Washington Post, August 12, 2021 Indeed, Samuel Wang, the director of the Princeton Gerrymandering Project, has concluded that if Republicans successfully gerrymander, they can win the House if the 2022 national popular vote rivals the 2020 Democratic edge of three points.

Can Open Data Save Redistricting Reform?

The American Prospect (2018)

Lawmakers Should Fix Inequitable District Lines

The Virginian-Pilot (2018). More detail here.

Princeton study predicts narrowing partisan margins in Georgia’s political makeup

Atlanta Journal-Constitution A Princeton University study of Georgia’s population found that the partisan gap between the state’s legislative and congressional districts has narrowed, with several seats potentially having competitive races next year

New York’s redistricting tests Democratic opposition to gerrymandering

Washington Post. September 2021.

“I think it’s pretty likely they draw a Democratic gerrymander,” said Adam Podowitz-Thomas of the Princeton Gerrymandering Project, a nonpartisan group that analyzes gerrymandering. “There’s not a huge political cost — when it comes to the ballot box no one picks a politician based on whether they gerrymandered or not.”

How will redistricting impact Georgia?

Atlanta Magazine According to an analysis by Fair Districts GA and the Princeton Gerrymandering Project, two-thirds of Georgia’s 85 small cities are divided into multiple House districts—often with split representation.

Can Math Stop Partisan Gerrymandering?

The Los Angeles Times (2017)

Citizen mapmakers honored for creative, but unofficial, redistricting efforts

"In some cases, entrants had only rudimentary mapping experience, but had substantial familiarity with local communities, underscoring the importance of public engagement within the mapping process and any public input periods following the upcoming release of redistricting maps," said Hannah Wheelen, data and technology lead for the Princeton Gerrymandering Project.

Data & Code (PGP)


A collaborative project to collect precinct geographies and election data from across all 50 states, D.C., and the five U.S. territories, to empower citizens in advance of the 2021 redistricting.

Gerrymandering Test Code (MATLAB)

Run the three gerrymandering tests presented on this site, and replicate the analyses reported in Three Tests for Practical Evaluation of Partisan Gerrymandering.

Virginia precincts and demonstrative map

Contains relevant precinct-level results and a demonstrative map for undoing the racially gerrymandered districts in the southeastern corner of Virginia. More detail at our GitHub repository.

Gerrymandering Test Code (Python)

Run the three gerrymandering tests presented on this site, as well as several other common gerrymandering metrics.

Geoprocessing Code

A loose collection of utilities for various geoprocessing operations that are common in the study of redistricting. Work in progress.

State Legislative Election Results, 1971–2018

Contains the results of over 80,000 single-member state legislative election from 1971 to 2016.

Congressional Election Results, 1948–2018

Cleaned results of each Congressional election from 1948 to 2016.

Useful Links


A community of interest mapping tool created by a team of Princeton undergraduates with help from PGP.

Runaway Redistricting: How the Rush to Redistricting Can Leave Communities Behind

With the adjusted census timeline, states will receive population data needed for redistricting several months later than in previous census cycles. Common Cause details, in this report, the likely impact of this new schedule; in addition to recommendations for ensuring a transparent and inclusive redistricting process.

Extreme Maps

A 2017 report by the Brennan Center on the district maps produced in the 2011 redistricting cycle.

Dave's Redistricting App

A free-to-use, public software for drawing and analyzing state legislative and congressional district plans.

All About Redistricting

A great resource maintained by Justin Levitt. Go here to find out, for instance, which parties controlled redistricting for various states in various years.


A free-to-use, public software created by the Metric Geometry and Gerrymandering Group for drawing state legislative and congressional district plans as well as communities.

The State of Redistricting Litigation

A tracker updated by the Brennan Center.

How Changes to the 2020 Census Timeline Will Impact Redistricting

A comprehensive analysis by the Brennan Center of how possible census delays will affect redistricting in 2020.


Visualize the efficiency gap across time, and upload custom district plans for analysis.

Scholarly Work

Data & Code (Non-PGP)

State Legislative Election Results

Carl Klarner's collection of state legislature elections from 1967–2016.

Daily Kos Elections Data

Daily Kos Elections maintains an archive of useful data on recent elections, including presidential election results by Congressional and State Legislative district, district maps, demographic information, and much more.


Code by Ben Fifield et al. to generate hundreds of thousands of alternative district plans.

Elections Geodata

An open-source effort to collect precinct-level geographic shapefiles.

Markov chain district sampler

C++ code by Wes Pegden et al. to sample among many similar district maps in order to determine if a map is highly unusual.


An open-source effort to collect precinct-level election results.


Python code by the Metric Geometry and Gerrymandering Group at Tufts to generate alternative districting plans.