Election boundary files contain data on the geographical boundaries of electoral districts, typically called precincts or wards.
The United States holds hundreds of elections every year, and boundaries may vary for each of them. These include primary elections, school board elections, and general elections for local, state, and federal offices. Election boundaries are drawn and results are certified by county boards.
Why this is important
Election results are used in analyses of the historic partisan performance of a single district or district plan. This is necessary for racially polarized voting analysis. It is also necessary to comply with some states’ competitiveness or partisan fairness criteria.
Election boundaries are essential to associate election results with specific geographies. This is necessary in order to evaluate the hypothetical past partisan performance of potential districts.
Who is included?
Election results and boundaries are typically maintained by the Board of Elections or equivalent agency in each county. Oftentimes, our partners must contact individual counties to collect data or clear up discrepancies.
Given that there are thousands of counties in the U.S., this process is incredibly time-consuming, especially when states do not have a process for maintaining standardized election results and precinct boundaries.
When is data collected?
The data is collected when someone votes. Some states allow early in-person voting, or conduct elections by mail and may receive ballots weeks in advance of Election Day. Many people vote on Election Day, and some states allow mail-in ballots to be counted up to several days after the election, provided they were postmarked by Election Day. Tabulating the results may take several days or even weeks, and there may be recounts or audits of the results before (or after) the results are certified (made final).
Election boundary files are maintained by counties. The smallest unit at which election results are typically reported are the precinct. Counties often change these precincts between elections, and previous boundary files are not always retained.
What information is collected?
Election results typically contain, for each election, every candidate’s name, the office for which they ran, their party affiliation, and the number of votes received by precinct. Election results may also indicate the number of votes received in person or by other voting methods.
Election boundary files contain geometric locations and geographic attributes.
How is this data collected?
Each state determines how its citizens vote. A handful of states conduct voting entirely by mail, and many other states allow no excuse absentee voting. All states provide for mail-in voting in some circumstances. In response to the COVID-19 pandemic, a number of states changed their election laws to expand eligibility for mail-in voting.
In rare cases, the state maintains election boundary files for all districts in the state. The majority of the time, however, the data must be collected by contacting each individual county.
How is this data processed?
Election data often must be converted from a long to wide format, so that the precincts are in the rows and the candidates (and their vote totals) are in the columns. In addition, column fields often need to be standardized across the counties and states.
Because each county maintains its own election boundary files, there is no standard file format; election boundary data come in the form of shps, pdfs, jpgs, and other formats.
Where can this data be found?
It varies by county. Election results are generally available online, but sometimes are emailed upon request, or must be obtained in person. Each county has its own way of posting results, which range from PDFs to CSVs to photos. Our Data Partners work hard to standardize these into a uniform format for every county in the nation.