A case study of congressional districting: “Rocks-Pebbles-Sand” approach

Abstract

As a case study into an algorithmic approach to congressional districting, North Carolina provides a lot to explore. Statistical modeling has called into question whether recent North Carolina district plans are unbiased. In particular, the literature suggests that the district plan used in the 2016 U.S. House of Representatives election yields outlier results that are statistically unlikely to be obtained without the application of bias. Therefore, methods for creating strong and fair district plans are needed. Informed by previous districting models and algorithms, we build a model and algorithm to produce an ensemble of viable Congressional district plans. Our work contributes a “Rocks-Pebbles-Sand” concept and procedure facilitating reasonable population equity with a small overall number of county splits among districts. Additionally, our methodology minimizes the initial need for granular, precinct-level data, thereby reducing the risk of covert gerrymandering. This case study indicates plausibility of an approach built upon an easy-to-understand intuition.