This week we hear from our Data Analyst, Hope Johnson, about the importance of our OpenPrecincts project, and the crucial role of precinct-level election data:

Precincts are the smallest level of election results. They are reported for state-wide races such as president, governor, and attorney general. Information from precincts can provide significant information about how people vote, and how districting plans impact political representation. However, until now, there has been no central data hub where browsers can find precinct-level shapefiles for all fifty states, Washington D.C., and the territories. Providing such data is the goal of OpenPrecincts, an open-source database of precinct-level shapefiles matched with current and historical election results.

A shapefile is a special kind of digital file format that is used by mapping programs. Shapefiles encode important information about location and geographic features, and are the foundation for many kinds of computer-assisted map-making and analysis.

To be useful in redistricting and gerrymandering analysis, precinct-level shapefiles must be matched with historical election results. However, states vary in their methods for compiling and publishing their precinct-level  shapefiles. Some states share this information online; others do not. Compiling and standardizing this information is an essential part of the OpenPrecincts project. Some of the data on OpenPrecincts was compiled and cleaned by the staff at the Princeton Gerrymandering Project. Other states were done by our partners at MGGG and VEST. 

The goal of OpenPrecincts is to publish a national database with 2016, 2018, and 2020 precincts matched with state-wide elections. As of this writing, twenty-five states have been processed.

In 2021, the American public will be presented with new maps of political districts across the country. In some places, these maps will likely be gerrymandered in favor of one political party or racial group. OpenPrecincts provides the data necessary to analyze these new maps, using precinct-level election results matched with shapefiles.

This type of analysis was effective in North Carolina in 2019. In that case, the Project used historical precinct-level election results from OpenPrecincts to estimate the partisan outcomes for nineteen proposed redistricting plans. Because of our access to granular election results and shapefiles, we were able to present an evidence-based comparison of the proposed redistricting plans in the Tar Heel State.

Indeed, OpenPrecincts can be used for many purposes. Precinct-level election results with matched shapefiles are a fruitful resource for analysts. For example, the Project used OpenPrecincts data to power a complex analysis of all possible redistricting outcomes in the state of Missouri. This type of analysis, known as MCMC sampling, is a powerful tool that allows users to see where one redistricting plan falls along a continuum of possibilities. 

OpenPrecincts is available to anyone, regardless of technical background or political leanings. The Project has made the code open-source, so that the public can view the steps we took in creating precinct-level election results matched with shapefiles. The documentation for each data set is visible on the state-specific pages, as seen in the image below.