How Do I Get The Area Of A Geojson Polygon With Python

I have the GeoJSON { 'type': 'FeatureCollection', 'features': [ { 'type': 'Feature', 'properties': {}, 'geometry': { 'type': 'Polygon', 'c

Solution 1:

It looks like geojson.io is not calculating the area after projecting the spherical coordinates onto a plane like you are, but rather using a specific algorithm for calculating the area of a polygon on the surface of a sphere, directly from the WGS84 coordinates. If you want to recreate it you can find the source code here.

If you are happy to carry on projecting the coordinates to a flat system to calculate the area, since it's good enough accuracy for your use case, then you might trying using this projection for Germany instead. E.g:

from osgeo import ogr
from osgeo import osr

source = osr.SpatialReference()
source.ImportFromEPSG(4326)

target = osr.SpatialReference()
target.ImportFromEPSG(5243)

transform = osr.CoordinateTransformation(source, target)

poly = ogr.CreateGeometryFromJson(str(geoJSON['features'][0]['geometry']))
poly.Transform(transform)
poly.GetArea()

which returns 87127.2534625642