These instructions create maps for the 119th Congress using district boundaries as of the 2024 elections. An example UI using maplibre-gl is in the example directory, and a Python lat/lng-to-district function is included.
Follow the steps below to create a web map of United States congressional districts from Census Bureau geospatial data. This year we are using Census Bureau data, but some years we use American Redistricting Project shapefiles when Census data is out of date.
Tippecanoe (2.17+) compiles the geospatial boundaries into a pmtiles file for efficiently serving vector tiles at various zoom levels.
On Ubuntu, you'll need node, GDAL, Tippecanoe, and this project's dependencies:
git clone https://github.com/govtrack/congress-maps.git
cd congress-maps
# node
curl -o- https://raw.githubusercontent.com/creationix/nvm/v0.31.0/install.sh | bash
nvm install stable
# GLAD
sudo apt install gdal-bin
# Tippecanoe
sudo apt install libprotobuf-dev protobuf-compiler libsqlite3-dev
git clone https://github.com/felt/tippecanoe # or download a release ZIP
cd tippecanoe
make -j
cd ..
# this repository's dependencies
npm install
To complete these steps, run the commands below.
# create directory to store data
mkdir data
# dowload district boundary data, unzip the data, and convert it to GeoJSON
wget -P data ftp://ftp2.census.gov/geo/tiger/TIGER2024/CD/tl_2024_*_cd119.zip
for fn in data/*_cd119.zip; do
unzip -oq $fn -d ./data/
ogr2ogr -f GeoJSON -t_srs crs:84 $(echo $fn | sed s/zip/geojson/) $(echo $fn | sed s/zip/shp/)
done
# normalize format and add label points, saving to data/map.geojson and data/bboxes.js
node process.js data/tl_2024*.geojson
# create vector tile cache from data
tippecanoe/tippecanoe \
-f -Z 0 -z 12 -B0 -pS \
-l layer -o data/cd-119-2024.pmtiles \
--name "119th Congress (2024 Election) Congressional Districts" \
data/map.geojsonDownload go-pmtiles https://github.com/protomaps/go-pmtiles/releases and select a Protomaps baselayer from https://maps.protomaps.com/builds/:
go-pmtiles_*/pmtiles extract https://build.protomaps.com/20250407.pmtiles example/baselayer.pmtiles --maxzoom=12 --region=united_states_region.geojson
That's enough to run the example.
Start a debug server:
node_modules/http-server/bin/http-server . --corsand visit http://127.0.0.1:8080/example.
When a map is loaded, querying the displayed map for what is under the mouse cursor is possible to do client-side (see the example). But it's only as good as the zoom level loaded.
It is possible to query the pmtiles data directly to find a congressional district by longitude/latitude since it basically is a geospatial index.
An example to do that in Python is included:
virtualenv venv
venv/bin/pip install pmtiles mapbox-vector-tile shapeley
venv/bin/python query.py data/cd-119-2024.pmtiles 12 -100 40
Note that the first argument is the zoom level to query at. It should be the max zoom level passed to tippecanoe with -z.