A variation on Mike Bostock's us-atlas (https://github.com/topojson/us-atlas) that includes quantized metro areas as a separate object

10m-all.json

build.sh

#!/bin/bash

# mad requirements:
npm install topojson-client topojson-server topojson-simplify shapefile ndjson-cli d3-geo-projection mapshaper -g

rm -rvf us
mkdir -p build us

# get both metros and counties
if [ ! -f build/cb_2015_us_cbsa_5m.shp ]; then
  curl -o build/cb_2015_us_cbsa_5m.zip 'https://www2.census.gov/geo/tiger/GENZ2015/shp/cb_2015_us_cbsa_5m.zip'
  unzip -od build build/cb_2015_us_cbsa_5m.zip cb_2015_us_cbsa_5m.shp cb_2015_us_cbsa_5m.dbf
  chmod a-x build/cb_2015_us_cbsa_5m.*
fi

if [ ! -f build/cb_2015_us_county_5m.shp ]; then
  curl -o build/cb_2015_us_county_5m.zip 'https://www2.census.gov/geo/tiger/GENZ2015/shp/cb_2015_us_county_5m.zip'
  unzip -od build build/cb_2015_us_county_5m.zip cb_2015_us_county_5m.shp cb_2015_us_county_5m.dbf
  chmod a-x build/cb_2015_us_county_5m.*
fi

# awkwardly build them all
geo2topo -q 1e5 -n counties=<( \
    shp2json -n build/cb_2015_us_county_5m.shp \
      | ndjson-filter '!/000$/.test(d.properties.GEOID)' \
      | ndjson-map '(d.id = d.properties.GEOID, delete d.properties, d)' \
      | geoproject -n 'd3.geoAlbersUsa().scale(1280).translate([480, 300])') \
  | toposimplify -f -p 0.25 \
  | topomerge states=counties -k 'd.id.slice(0, 2)' \
  | topomerge nation=states \
  > us/10m.json

geo2topo -q 1e5 -n  metros=<( \
    shp2json -n build/cb_2015_us_cbsa_5m.shp \
      | ndjson-filter '!/000$/.test(d.properties.GEOID)' \
      | ndjson-map '(d.id = d.properties.GEOID, delete d.properties, d)' \
      | geoproject -n 'd3.geoAlbersUsa().scale(1280).translate([480, 300])') \
  | toposimplify -f -p 0.25 \
  > us/10m-metros.json
  
mapshaper -i combine-files us/10m.json us/10m-metros.json -o us/10m-all.json