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

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 election outcome 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 additional districts in which that party potentially could have been competitive, without losing any currently won districts, by making reasonable changes to the input map. With the GEO metric, we can also indicate which districts were likely packed, and indicate which districts in the GEO metric count are the most likely to have been cracked. We then analyze GEO metric scores for each party in several recent elections.