Here are details from the readme:
GeoJSON and other shape files for the federal legislative districts of the US.
Shapes for state legislative districts
Using the shapes
All files in this repository are automatically published to theunitedstates.io, at predictable URLs.
For example, GeoJSON for New York’s 1st district can be found at:
The 2012 here refers to the year that these districts came into effect, and is the most current districts. “At Large” districts, where only 1 person represents an entire state or territory, are coded with a district number of 0 (e.g. WY-0 and PR-0).
GeoJSON for the state of New York can be found at:
Replace .geojson with .kml to get a KML version of a district.
You can also download the entire set as a ZIP file, and use them however you like. If you plan on using these for heavy traffic, or you want control over the domain name they live on, you should use this method.[…]
Eric points us to this example of a shape file rendered in the browser: https://github.com/unitedstates/districts/blob/gh-pages/cds/2012/AR-3/shape.geojson
For more details, please see the readme.
The unitedstates Project is “a shared commons of data and tools for the United States.” It was created by Eric Mill, Joshua Tauberer, and Derek Willis.