Pennsylvania Congressional Districts

« Back


50-State Simulation Project Team

Last updated

July 16, 2024


« Back

Pennsylvania has 17 congressional districts. We’ve generated 5,000 sets of randomly simulated districts according to the relevant criteria. Three of these plans are shown here, along with the actual enacted map.

Partisan Features

In Pennsylvania, Democrats win about 52% of the vote in a typical statewide election. Proportionally, that would translate to 8.9 Democratic seats out of 17 total.

But proportionality isn’t guaranteed, even in a fair redistricting process. In our simulated plans, Democrats won anywhere from 7.4 to 8.9 seats on average, with 8.1 being the most typical. In contrast, we expect the enacted plan to yield 9.3 Democratic seats on average, which is more than 100% of all simulated plans.

The graph below breaks this down in detail, showing how each district of the enacted plan compares to the set of simulated districts.

Gerrymandering metrics

There are other ways of measuring the partisan skew of redistricting plan. The graph below shows two these metrics. The deviation from partisan symmetry measures the expected difference in each party’s share of seats if they each won 50% of the statewide vote. The efficiency gap is calculated as the difference in the number of wasted votes for each party.

Learn more about these metrics here.

Traditional redistricting criteria

Factors other than partisanship are important for redistricting, too. The graph below shows the geographic compactness and the number of counties which are split into multiple districts. As far as compactness, Pennsylvania’s enacted plan scores a 0.32, more than 100% of all simulated plans (a higher score means more compact). It splits 14 counties, compared to an average of 12 counties for our simulated plans.

Political Geography

These two maps show the partisan lean across Pennsylvania in a typical statewide election, and the share of minority voters around the state.

More information

Download the data for Pennsylvania.

Learn more about our methodology.

Elections included in analysis:

  • President 2016
  • US Senate 2016
  • Attorney General 2016
  • US Senate 2018
  • Governor 2018
  • President 2020
  • Attorney General 2020

Redistricting requirements

Our algorithmic constraints used in simulations are in part are based on some of these requirements and discretionary criteria. See full documentation and code for the complete implementation details.

In Pennsylvania, there are few formal districting requirements, but districts must generally:

  1. be contiguous
  2. have equal populations
  3. be geographically compact
  4. preserve county and municipality boundaries as much as possible