Municipalities Can Matter: A Case Study of Redistricting in Pennsylvania

Pennsylvania is my home state, and has been panned in the past for the shapes of its districts, including the famous “Goofy Kicking Donald Duck” in the 2010 congressional redistricting. In the process of doing an analysis using different techniques separate than those involved in League of Women Voters v. Commonwealth of PA, we uncovered new information concerning different assumptions made in the sampling process: the role of preserving as many townships as possible.

The 2010 redistricting was declared unconstitutional at the state level, and has since been redrawn. An MCMC analysis of this redistricting, as well as a number of the proposed alternative maps, found that the 2010 redistricting plan was indeed a partisan gerrymander, but there were a few disagreements between our results and the results used in the court case. Careful inspection of a few key areas of PA led to a potential conclusion: global sampling methods can split communities that local sampling methods may not. This includes places such as State College, home to Penn State. It is thus interesting to ask: if we force townships and other communities to be preserved, will the results change? It turns out that forcing preservation gave results more in line with local methods. This phenomena has, to the best of our knowledge, not been previously observed in the literature.

These results have been presented at the 2018 SAMSI Workshop on Quantifying Gerrymandering, and a preprint shall be released soon.