Make Zip code boundaries in Google Map API

Question

I have seen all the responses to a similar question, however, they are all either old, or no one has answered them.

I have been given the task to obtain zip codes and di

Answer 1

DOwnload the shapefile from here https://catalog.data.gov/dataset/tiger-line-shapefile-2019-2010-nation-u-s-2010-census-5-digit-zip-code-tabulation-area-zcta5-na

Simplifying using GDAL

We can use the ogr2ogr command from the GDAL library to convert the shapefile to geojson but even with only one field and simple coordinates the output file is over 1GB.

ogr2ogr -f GeoJSON -select ZCTA5CE10 -lco COORDINATE_PRECISION=6 zcta.geojson /vsizip/tl_2017_us_zcta510.zip

I tried to simplify this to topojson, but the topojson library chokes on this even on a very powerful 2017 MacBook Pro.

npx topojson -q 1e4 -o zcta_topo.json zcta.geojson >> JavaScript head out of memory

Another method I tried was using the -simplify option in ogr2ogr. The simplify argument is a unit of measure based on the spatial reference system of the shapefile. Since the srs for the ZCTAs is WGS84 the unit is a lat/lon measure.

ogr2ogr -f "GeoJSON" -lco COORDINATE_PRECISION=6 -select ZCTA5CE10 -simplify 0.006 zcta.geojson /vsizip/tl_2017_us_zcta510.zip

This creates a much smaller GeoJSON file (30MB) which the TopoJSON can easily handle and we end up with a more managable (but still too large) 13MB topojson file. Additionally, the topology of the dataset is very poor at medium to large scales.

npx topojson -q 1e5 -o zcta_topo.json zcta.geojson

Simplifying using Postgis

Create a docker volume to use for persistence docker volume create postgresql

Run the postgis docker

docker run --name postgis -p 25432:5432 -it --mount source=postgresql,target=/var/lib/postgresql kartoza/postgis

Load the zcta shapefile into postgis

ogr2ogr -f "PostgreSQL" -progress -select "ZCTA5CE10" -overwrite -lco OVERWRITE=yes -nln zcta -nlt PROMOTE_TO_MULTI -t_srs "EPSG:4326" PG:"dbname='gis' host='localhost' port='25432' user='docker' password='docker'" ~/Downloads/tl_2017_us_zcta510/tl_2017_us_zcta510.shp

Sample query with st_simplifypreservetopology (New England). This takes a long time to run for the entire country and we still lose a lot of the topology.

select st_simplifypreservetopology(wkb_geometry, 0.025) as thegeom, zcta5ce10 from zcta where zcta5ce10 like '0%' OR zcta5ce10 like '1%'

Simplifying using Mapshaper (Best solution)

The Mapshaper library can output TopoJSON directly from the shapefile without JavaScript memory heap errors. This command creates a ~6MB topojson file that we can use. It also manages to keep topology very well by assuming that very close verticies and edges should be coincident.

npx -p mapshaper mapshaper-xl tl_2017_us_zcta510.shp snap -simplify 0.1% -filter-fields ZCTA5CE10 -rename-fields zip=ZCTA5CE10 -o format=topojson zcta_mapshaper.json

source:https://github.com/elastic/ems-file-service/issues/6