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Is it possible to get counts of intersections between two geometries using GeoPandas objects? That is, I want to count up the number of polygons or line strings in one GeoDataFrame that intersect with each polygon in another GeoDataFrame. I did not see an easy way of doing this while browsing the GeoPandas docs, but wanted to check before moving on to lower-level tools.

Chris Fonnesbeck
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  • https://stackoverflow.com/questions/54127731/how-can-i-count-the-number-of-polygons-a-shape-intersects – swatchai Apr 21 '21 at 16:59

3 Answers3

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You want a spatial join: geopandas.tools.sjoin().

There's an example in this Jupyter Notebook — look at the section called Spatial join. This is counting a set of points (midpoints) into a set of polygons (bins). Both geometries define a GeoDataFrame.

At the time of writing, tools.sjoin() is not in the current release of geopandas. I couldn't get geopandas.tools to build in any of their branches, but I fixed it — for me anyway — in my fork. My fix is an open PR.

Matt Hall
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I don't know about a built-in tool to do this but I'm not an expert. At the same time it's easily done with some pandas magic:

import geopandas as gpd
from shapely.geometry import *

p1 = Point(.5,.5)
p2 = Point(.5,1)
p3 = Point(1,1)

poly = Polygon([(0,0), (0,2), (2,2), (2,0)])

df1 = gpd.GeoSeries([p1,p2,p3])
df2 = gpd.GeoDataFrame([poly,p3], columns=['geometries'])

f = lambda x:np.sum(df1.intersects(x))
df2['geometries'].apply(f)

Should return:

0    3
1    1
Name: geometries, dtype: int64
Fabzi
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Lets consider 02 geometries (Points and Polygons) which intersect at least once.

  1. Spatial join of your layers

You should write something like this : pointsInPolygon = gpd.sjoin(points, polygons, how="inner", op='intersects')

  1. Add a field with 1 as a constant value You should write something like this : pointsInPolygon['const']=1

  2. Group by the field according to the column by which you want to aggregate data You should write something like this : pointsInPolygon.groupby(['field']).sum()

The column [const] will give you the count of intersections between your two geometries.

If you want to see others columns as well, just type something like this : df = pointsInPolygon.groupby('field').agg({'columnA':'first', 'columnB':'first', 'const':'sum'}).reset_index()

Yannick Arthur DOUNGMO
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