The Geography and Election Outcome (GEO) Metric: An Introduction

Abstract: We introduce the Geography and Election Outcome (GEO) metric, a new method for identifying potential partisan gerrymanders. In contrast with currently popular methods, the GEO metric uses both geographic information about a districting plan as well as district-level partisan data, rather than just one or the other. We motivate and define the GEO metric, which gives a count (a non-negative integer) to each political party. The count indicates the number of previously lost districts which that party potentially could have had a 50% chance of winning, without risking any currently won districts, by making reasonable changes to the input map. We then analyze GEO metric scores for each party in several recent elections. We show that this relatively easy to understand and compute metric can encapsulate the results from more elaborate analyses.