Script for creating topojson of congressional districts

create_districts_topo.sh

SOURCE_FILE=src/tl_2016_us_cd115.shp # unzipped http://www2.census.gov/geo/tiger/TIGER2016/CD/tl_2016_us_cd115.zip to ./src/
OUT_FILE=new_districts.json
SIMP_PARAM=0.015 # lower value = more simplification, ref: https://github.com/topojson/topojson-simplify/blob/master/README.md#toposimplify_spherical_quantile
QUANTIZE_PARAM=1e5
PATH=$(npm bin):$PATH

# Process based on https://medium.com/@mbostock/command-line-cartography-part-3-1158e4c55a1e

set -eu

shp2json $SOURCE_FILE | \
  # convert to ndjson
  ndjson-split 'd.features' | \
  # Only keep features that have strictly numeric GEOID props
  # because some of them have "ZZ" in their GEOID
  ndjson-filter '/^\d+$/.test(d.properties.GEOID)' | \
  # assign integer id based on the original GEOID string
  ndjson-map 'd.id = parseInt(d.properties.GEOID, 10), d' | \
  # remove all properties
  ndjson-map 'd.properties = {}, d' > .tmp.ndjson

# covert to topojson and simplify + quantize
geo2topo -n districts=.tmp.ndjson | \
  toposimplify -S $SIMP_PARAM -f | \
  topoquantize $QUANTIZE_PARAM > $OUT_FILE

rm .tmp.ndjson
ls -alh $OUT_FILE

package.json

{
  "dependencies": {
    "ndjson-cli": "^0.3.0",
    "shapefile": "^0.6.2",
    "topojson": "^3.0.0",
    "topojson-client": "^3.0.0",
    "topojson-server": "^3.0.0",
    "topojson-simplify": "^3.0.1"
  }
}

1. Clone this gist or copy these files to a directory
2. Download http://www2.census.gov/geo/tiger/TIGER2016/CD/tl_2016_us_cd115.zip and unzip it to a subdirectory called src/
3. run npm install to install required tools
4. run ./create_districts_topo.sh to create new_districts.json. You might have to make the script executable first: chmod +x create_districts_topo.sh.