Applying custom spatial operations

Working with Geospatial Data in Python

Joris Van den Bossche

Open source software developer and teacher, GeoPandas maintainer

Total river length within 50 km of each city?

For a single point (cairo):

area = cairo.buffer(50000)

rivers_within_area = rivers.intersection(area)

print(rivers_within_area.length.sum() / 1000)

186.397219642

The apply() method

Series.apply(): call a function on each of the values of the Series

Series.apply(function, **kwargs)

function: the function being called on each value; the value is passed as the first argument
**kwargs: additional arguments passed to the function

For a GeoSeries, the function is called as function(geom, **kwargs) for each geom in the GeoSeries

Applying a custom spatial operation

The function to apply:

def river_length(geom, rivers):
    area = geom.buffer(50000)
    rivers_within_area = rivers.intersection(area)
    return rivers_within_area.length.sum() / 1000

Call function on the single geometry:

river_length(cairo, rivers=rivers)

186.3972196423455

Applying on all cities:

cities.geometry.apply(river_length, rivers=rivers)

Applying a custom spatial operation

Applying on all cities:

cities.geometry.apply(river_length, rivers=rivers)

0        0.000000
1        0.000000
2      106.072198
          ...

Applying a custom spatial operation

Applying on all cities and assigning result to new column:

cities['river_length'] = cities.geometry.apply(river_length, rivers=rivers)
cities.head()

             name                       geometry  river_length
0    Vatican City    POINT (1386304.6 5146502.5)      0.000000
1      San Marino    POINT (1385011.5 5455558.1)      0.000000
2           Vaduz    POINT (1059390.7 5963928.5)    106.072198
..            ...                            ...           ...

Let's practice!

Working with Geospatial Data in Python