Jeffrey B. Lewis, Brandon DeVine, and Lincoln Pritcher with Kenneth C. Martis
The webpage for this project can be found at https://cdmaps.polisci.ucla.edu.
This repository provides digital boundary definitions in GeoJson format for every U.S. Congressional District in use between 1789 and 2025. These were produced as part of NSF grant SBE-SES-0241647 between 2009 and 2013, augmented with boundaries published by the US Census Bureau or state-level agencies since then.
This is the new Version 2.0 repository. Like the previous version, it contains definitions for every Congressional district used throughout the history of Congress in GeoJSON format. In the previous release, the GeoJSON files were lower-resolution versions of the shapefiles found on the website provided on GitHub, provided for quick quality checking and for making maps. In this new release, the GeoJSON files provide the same (higher) resolution as the shapefiles. The GeoJSON files are also the canonical representation of the data that we will be updating moving forward (the project had previously been managed in PostGIS). The shapefiles presented on the website are now generated from the GeoJSON here.
Updates and maintenance of the collection moving forward uses thetargets
workflow manager in R and a simple patching system. All of the
code used is provided in this repository.
We have done a good deal of work to validate all of the shapes. However, some irregularities likely remain. Please email jblewis@ucla.edu with questions or suggestions for improvement.
Many districts were formed by aggregating complete county shapes obtained from the National Historical Geographic Information System (NHGIS) project and the Newberry Library's Atlas of Historical County Boundaries. Where Congressional District boundaries did not coincide with county boundaries, district shapes were constructed district-by-district using a wide variety of legal and cartographic resources. Detailed descriptions of how particular districts were constructed and the authorities upon which we relied are available (at the moment) by request.
The Principal Investigator on the project was Jeffrey B. Lewis. Brandon DeVine and Lincoln Pitcher researched district definitions and produced thousands of digital district boundaries. The project relied heavily on Kenneth C. Martis' The Historical Atlas of United States Congressional Districts: 1789-1983. (New York: The Free Press, 1982). Martis also provided guidance, advice, and source materials used in the project.
Jeffrey B. Lewis, Brandon DeVine, Lincoln Pitcher, and Kenneth C. Martis. (2013) Digital Boundary Definitions of U.S. Congressional Districts, 1789-2012. [Data file and code book]. Retrieved from http://cdmaps.polisci.ucla.edu on [date of download].
If you use the shapes in your research, please send an email describing your project and giving citations to related working papers and publications.
The district definitions are organized by state and the range of Congresses in which they were operative. Each unique district has been given a unique identifier with the following format SSNNBBBEEE where SS is the state FIPS code, NN is the district number, BBB is the number of the first Congress in which that district was used and EEE is the last Congress in which that district was used.
District geographic definitions are encoded in US Census standard unprojected format using the NAD83 coordinate datum (PostGIS SRID 4269). The PROJ.4 string is:
+proj=longlat +ellps=GRS80 +towgs84=0,0,0,0,0,0,0 +no_defs Download
The files provide district shapes for each Congress in ERSI's Shapefile format. The current files are version 1.00 (June 20, 2013).
Our enumeration of Congressional districts in effect in a particular Congress follows Martis. At large districts are numbered "0". In a few cases, shapes describing Indian territories within states during the 18th and early 19th centuries are included in the shape files. These territories are always assigned district number "-1". The Congressional districts in the shape files match districts contained in rollcall voting data files and Congressional roster files available on Keith Poole's Voteview site here and here. There are a very few instances in which there is no member representing a particular district in a particular Congress (a file enumerating all known discrepancies between the Voteview data and these shapes is available here.
Starting with the 103rd Congress, district boundary files are produced by the US Census, and we rely on those shapes for Congresses beginning with the 103rd. US Census Tigerline files associated with the 1990 Decennial Census were used to construct districts from the 98th to the 102nd Congress (except where noted in the documentation files below). For Congresses between the 1st and the 97th, district boundaries were formed in one of two ways. For districts that were made up of collections of complete counties, historical county boundaries from NHGIS or were dissolved to form district boundaries. Districts that divided one or more counties were formed on a case-by-case basis. Sources relied upon for these districts are described in the documentation files below.
Access to Excel .xlsx files containing references and documentation related to how each district shape was drawn is available at http://cdmaps.polisci.ucla.edu. Access to these files is limited due to possible copyright issues (some of the documentation files include images of maps). To obtain access to these materials for research purposes, please email jblewis@ucla.edu.
Copyright Jeffrey B. Lewis, 2025.