Political Districting to Minimize County Splits

When partitioning a state into political districts, a common criterion is that political subdivisions, like counties, should not be split across multiple districts. This criterion is encoded into most state constitutions and is sometimes enforced quite strictly by the courts. However, map drawers, courts, and the public typically do not know what amount of splitting is truly necessary, even to satisfy basic criteria, like contiguity and population balance. In this paper, we provide answers for all congressional, state senate, and state house districts in the United States using 2020 census data. Our approach is based on integer programming. The associated codes and experimental results are available on GitHub.

Funding: This material is based upon work supported by the National Science Foundation [Grant 1942065].

Supplementary Material: All supplemental materials, including the computer code that supports the findings of this study, are available at https://doi.org/10.1287/opre.2023.0094.