Digitizing, Districting, and Data - Creating an Open Source Precinct Shapefile for Ohio

Presented by:
Katie Jolly & Katya Kelly (Macalester College)
Abstract:

One of the most recent advances in voting rights research has been the use of GIS and computation to create new metrics for fairness of maps. Voting precinct shapefiles are necessary in order to spatially evaluate election results, bring gerrymandering cases to court, and create viable alternative districting plans. Even as more government data has been made public over the last few years, many counties still do not publish their precinct boundaries in an accessible format. Ohio is particularly challenging for precinct shapefile collection. As part of a larger project, we set out to create an open-source, statewide shapefile from county shapefiles or PDFs. In a handful of counties, there were neither. Instead we developed a methodology that uses geocoded addresses from the public voter file to approximate precinct boundaries. In theory, precinct boundaries do not split census blocks, so we wrote a nearest neighbor classification algorithm to allocate blocks to precincts. This method loses some of the accuracy of digitizing PDFs but saves considerable time and produces comparable results. As the 2020 census and election approach, the implications of districting plans become more important to understand. Drawing precinct boundaries is a first step, and this project aims to make that process easier for future researchers and community members.