Saving Overpass query results to GeoJSON file with Python

Question

I have just started to use Python and I would like to make a query to Overpass and store the results in a geospatial format (e.g. GeoJSON).

As far as I know, there is a library called overpy that should be what I am looking for. After reading its documentation I came up with the following code:

import overpy

API = overpy.Overpass()

# Fetch highways within Granollers' city.

result = API.query("""
    area[name="Granollers"][admin_level=8];
    // query part for: “highway=*”
    (way["highway"](area);
    relation["highway"](area);
    );
    // print results
    out body;
    """)

The thing is that I am not familiar at all with python and I don't know how to store result as a GeoJSON file (Honestly, I don't even know what kind of thing result is -I tried with type(result) and I get overpy.Result as an output, which doesn't mean much to my poor knowledge). I have been reading overpy documentation but I haven't been able to figure it out.

Answer 1

You could do this using overpass that already returns a geojson object and then, if you want, you can use the geojson package to convert this object into str (string object) or save it in a file.

import overpass
import geojson

api = overpass.API()

# api.get already returns a FeatureCollection, a GeoJSON type
res = api.get("""
    area[name="Granollers"][admin_level=8];
    // query part for: “highway=*”
    (way["highway"](area);
      relation["highway"](area);
    );
    // recurse down to get the nodes, required for the geometry
    (._;>;);
""")

# if you want a str, then use dumps function
#geojson_str = geojson.dumps(res)

# dump as file, if you want to save it in file
with open("./test.geo.json",mode="w") as f:
  geojson.dump(res,f)

OBS: Take a look at the line with (._;>;); it is VERY important for the example you provide. Your query is about ways and relations, and if you don't add the last line to the query, the server will respond with ways and relations but no nodes and therefore won't be coordinates and without coordinates, the resulting geojson won't have geometries at all.

Finally, be aware that this query retrieves almost 2 MB of data, so consider this when you try to handle the results.

Answer 2

To export a valid 'line'-geojson you could set the verbosity to 'geom'. If you are facing timeout issues you could set a larger timeout value than the default 25.

import overpass
import geojson

api = overpass.API(timeout=500)

# api.get already returns a FeatureCollection, a GeoJSON type
res = api.get("""
    area[name="Granollers"][admin_level=8];
    // query part for: “highway=*”
    (way["highway"](area);
      relation["highway"](area);
    );
""", verbosity='geom')

# dump as file, if you want to save it in file
with open("c:/temp/testio.geojson",mode="w") as f:
  geojson.dump(res,f)