Networks for OSM Boundaries

Last update

October 15, 2024

If you want to download a street network for a specific OSM boundary then you can use osmnx to download the boundary, which can then be passed to cityseer for generating a network.

Download Boundary

Download the boundary. Go to OSM and select the relation ID for the boundary that you’d like to download and pass it to ox.geocode_to_gdf().

import osmnx as ox

bounds_gdf = ox.geocode_to_gdf(
    "R1536593",  # OSM relation ID
    by_osmid=True,
)
# optionally use to_crs() to project to a target CRS
# returns a geoDataFrame - union for the geom
bounds_geom = bounds_gdf.union_all()
bounds_geom

Tip

You can optionally project to a required CRS by using geopandas to_crs() methodo before taking the union. This is generally recommended if you want to apply a buffer to the geometry (assuming a unit such as metres).

Buffer and Simplify

Buffer and simplify depending on preferences. Make sure your distances correspond to the unit of the current CRS!

# buffer if wanted
bounds_geom = bounds_geom.buffer(0.01)  # WGS - 4326
# some simplification is recommended
# otherwise the request to the underlying API used by io.osm_graph_from_poly()
# might complain that the boundary description is too long
bounds_geom = bounds_geom.simplify(
    0.001  # WGS - 4326
)  # here the CRS unit is degrees hence the small number
bounds_geom

Generate Network

Now you can pass the boundary to cityseer to download and create the network.

from cityseer.tools import io, plot

G_nx = io.osm_graph_from_poly(
    bounds_geom,
    # 4326 by default - use projected CRS instead if you projected your GDF
    poly_crs_code=4326,
    simplify=False,  # set to True for automatic simplification
)
plot.plot_nx(G_nx, plot_geoms=True)

INFO:cityseer.tools.io:Converting networkX graph from EPSG code 4326 to EPSG code 32631.
INFO:cityseer.tools.io:Processing node x, y coordinates.
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INFO:cityseer.tools.io:Processing edge geom coordinates, if present.
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INFO:cityseer.tools.graphs:Generating interpolated edge geometries.
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INFO:cityseer.tools.graphs:Removing filler nodes.
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INFO:cityseer.tools.graphs:Ironing edges.
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INFO:cityseer.tools.graphs:Merging parallel edges within buffer of 1.
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INFO:cityseer.tools.plot:Preparing graph nodes
INFO:cityseer.tools.plot:Preparing graph edges
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