United States Precinct Boundaries and Statewide Partisan Election Results.

We describe the creation and verification of databases of all precinct boundaries used in the United States 2016, 2018, and 2020 November general elections, enhanced with election results for all partisan statewide offices. United States election officials report election results in the smallest geographic reporting known as the precinct. Scholars and practitioners find these election results valuable for numerous use cases. However, these data cannot be augmented with other geographically-bound data, such as U.S. Census data, without precinct boundaries. Here we describe the collection of precinct boundary data from state and local election officials, sometimes provided in GIS formats, images, text descriptions, and - in rare cases - verbally. We describe how we verify boundaries with other election data, such as geocoded voter registration files. Our open-source data has appeared in redistricting litigation argued before the United States Supreme Court; and has been used by state and local redistricting authorities, media organizations, advocacy groups, scholars, and a vibrant community of mapping enthusiasts.