Adding a background map to plots

This example shows how you can add a background basemap to plots created with the geopandas .plot() method. This makes use of the contextily package to retrieve web map tiles from several sources (OpenStreetMap, Stamen).

# sphinx_gallery_thumbnail_number = 3
import geopandas

Let’s use the NYC borough boundary data that is available in geopandas datasets. Plotting this gives the following result:

df = geopandas.read_file(geopandas.datasets.get_path('nybb'))
ax = df.plot(figsize=(10, 10), alpha=0.5, edgecolor='k')

Convert the data to Web Mercator

Web map tiles are typically provided in Web Mercator (EPSG 3857), so we need to make sure to convert our data first to the same CRS to combine our polygons and background tiles in the same map:

df = df.to_crs(epsg=3857)

Contextily helper function

We define a small helper function that uses contextily to add a map as background to an existing plot:

import contextily as ctx

def add_basemap(ax, zoom, url=''):
    xmin, xmax, ymin, ymax = ax.axis()
    basemap, extent = ctx.bounds2img(xmin, ymin, xmax, ymax, zoom=zoom, url=url)
    ax.imshow(basemap, extent=extent, interpolation='bilinear')
    # restore original x/y limits
    ax.axis((xmin, xmax, ymin, ymax))

Add background tiles to plot

Now we can use the above function to easily add a background map to our plot. The zoom keyword is required and let’s you specify the detail of the map tiles (be careful to not specify a too high zoom level, as this can result in a large download):

ax = df.plot(figsize=(10, 10), alpha=0.5, edgecolor='k')
add_basemap(ax, zoom=10)

By default, contextily uses the Stamen Terrain style. We can specify a different style using ctx.sources:

ax = df.plot(figsize=(10, 10), alpha=0.5, edgecolor='k')
add_basemap(ax, zoom=11, url=ctx.sources.ST_TONER_LITE)

Total running time of the script: ( 0 minutes 3.384 seconds)

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