District Populations and Partisan Bias

We investigate whether the differing population sizes of legislative districts affect the ability to engage in partisan gerrymandering. We conjecture that larger populations facilitate partisan gerrymandering by providing mapmakers with more “raw material” to manipulate, and this might make such districts less compact. Evidence based on measures of partisan bias, district population, and compactness suggests that more populous districts encourage partisan distortion and do so partly through violations of compactness. Regression analysis of lower and upper chamber state legislative maps shows that more populous districts lead to more partisan bias in maps even after accounting for other aspects of districts and Voting Rights Act requirements that affect how states draw district lines.