Creative Commons Attribution 4.0 International license
In the process of redistricting, one important metric is the number of competitive districts, that is, districts where both parties have a reasonable chance of winning a majority of votes. Competitive districts are important for achieving proportionality, responsiveness, and other desirable qualities; some states even directly list competitiveness in their legally-codified districting requirements. In this work, we discuss the problem of drawing plans with at least a fixed number of competitive districts. In addition to the standard, "vote-band" measure of competitivenesss (i.e., how close was the last election?), we propose a measure that explicitly considers "swing voters" - the segment of the population that may choose to vote either way, or not vote at all, in a given election. We present two main, contrasting results. First, from a computational complexity perspective, we show that the task of drawing plans with competitive districts is NP-hard, even on very natural instances where the districting task itself is easy (e.g., small rectangular grids of population-balanced cells). Second, however, we show that a simple hill-climbing procedure can in practice find districtings on real states in which all the districts are competitive. We present the results of the latter on the precinct-level graphs of the U.S. states of North Carolina and Arizona, and discuss trade-offs between competitiveness and other desirable qualities.
@InProceedings{chuang_et_al:LIPIcs.FORC.2024.7,
author = {Chuang, Gabriel and Hanguir, Oussama and Stein, Clifford},
title = {{Drawing Competitive Districts in Redistricting}},
booktitle = {5th Symposium on Foundations of Responsible Computing (FORC 2024)},
pages = {7:1--7:22},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-319-5},
ISSN = {1868-8969},
year = {2024},
volume = {295},
editor = {Rothblum, Guy N.},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.FORC.2024.7},
URN = {urn:nbn:de:0030-drops-200902},
doi = {10.4230/LIPIcs.FORC.2024.7},
annote = {Keywords: Redistricting, Computational Complexity, Algorithms}
}