TopoJSON to GeoJSON converter

topo2geojson.py

"""
topo2geojson.py
Convert topojson to geojson

Example Usage:
  python topo2geojson.py data.topojson data.geojson 


The topojson tested here was created using the mbostock topojson CLI
created with --spherical coords and --properties turned on

Author: Matthew Perry (http://github.com/perrygeo)
Thanks to @sgillies for the topojson geometry logic
requires:
  https://github.com/sgillies/topojson/blob/master/topojson.py

Next steps: how can this be generalized to a robust CLI converter?
"""
import json
import sys
from topojson import geometry
from shapely.geometry import asShape

topojson_path = sys.argv[1]
geojson_path = sys.argv[2]

with open(topojson_path, 'r') as fh:
    f = fh.read()
    topology = json.loads(f)

# file can be renamed, the first 'object' is more reliable
layername = topology['objects'].keys()[0]  

features = topology['objects'][layername]['geometries']
scale = topology['transform']['scale']
trans = topology['transform']['translate']

with open(geojson_path, 'w') as dest:
    fc = {'type': "FeatureCollection", 'features': []}

    for id, tf in enumerate(features):
        f = {'id': id, 'type': "Feature"}
        f['properties'] = tf['properties'].copy()

        geommap = geometry(tf, topology['arcs'], scale, trans)
        geom = asShape(geommap).buffer(0)
        assert geom.is_valid
        f['geometry'] = geom.__geo_interface__
        
        fc['features'].append(f) 

    dest.write(json.dumps(fc))

toposimplify.sh

!#/bin/bash

echo "Convert ESRI File Geodatabase to a shapefile in Plate Carre/WGS84 (EPSG:4326)"

ogr2ogr -t_srs epsg:4326 -f "ESRI Shapefile" \
    ecoregions_original.shp EcoregionSummaries3.gdb.zip EcoSums_ForMatt

echo "Convert shapefile to topojson with simplification"
# -s <tolerance> measured in steridians
# see http://en.wikipedia.org/wiki/Steradian#SI_multiples
# alternatively, can specify proportion of points kept
# e.g. --simplify-proportion 0.1 \

# rm temp*
for tolerance in 1E-7 1E-8 1E-9 1E-10
    do
        topojson --spherical \
            --properties \
            -s $tolerance \
            -q 1E6 \
            -o temp_$tolerance.topojson \
            ecoregions_original.shp &&

        # Convert it to GeoJSON
        python topo2geojson.py temp_$tolerance.topojson temp_$tolerance.geojson &&

        # Optionally, convert GeoJSON to any OGR data source
        ogr2ogr -f "ESRI Shapefile" ecoregions_$tolerance.shp temp_$tolerance.geojson OGRGeoJson &

    done
    wait

This was really useful! Used it to plot some covid-19 data across South Africa

5 years later I made a CLI from this to convert topojson to geojson. Check it out here: https://github.com/kylepollina/topo2geo
Thank you!

@kylepollina Yesss!!!!

I'm porting the whole TopoJSON suit from Mike Bostock. You can install it running:

pip install pytopojson

You can convert from TopoJSON either with the command-line tool:

python bin/topo2geo.py aruba=- < topojson.json

Or inside a script:

from pytopojson import feature

topojson = {
  "type": "Topology",
  "transform": {
    "scale": [0.036003600360036005, 0.017361589674592462],
    "translate": [-180, -89.99892578124998]
  },
  "objects": {
    "aruba": {
      "type": "Polygon",
      "arcs": [[0]],
      "id": 533
    }
  },
  "arcs": [
    [[3058, 5901], [0, -2], [-2, 1], [-1, 3], [-2, 3], [0, 3], [1, 1],
     [1, -3], [2, -5], [1, -1]]
  ]
}

feature_ = feature.Feature()
geojson = feature_(topojson, 'aruba')

thank you. (off topic) also planning to use this in another platform. any chance you guys know java? there is no lib to convert topojson to geojson in java, sadly.