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I have recently started using Geopandas and am having a problem with the performance of intersects. The intersect tests whether land parcels have a road within (or across the boundary).

Parcel data (parcels) is a polygon geodataframe and roads (roads) are as a line geodataframe. I attempt to find out if the parcel interacts with a road with the follwoing code:

road = roads.unary_union
parcels['road_intersection'] = parcels.intersects(road)

Here I generate get a column 'road_intersection' with True/False values.

with 985 parcel polygons and 20854 road lines, this takes over a minute to generate a result.

I have previously tried with 

parcels['road_intersection'] = parcels.intersects(roads)

but this did not seem to test all roads with all parcels.

Would anyone be able to provide any tips for correct use or optimisation?

PolyGeo
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Mr_Robinini
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1 Answers1

6

For intersections in GeoPandas, it is better to use a spatial-join (see More Efficient Spatial join in Python without QGIS, ArcGIS, PostGIS, etc or How to efficiently determine which of thousands of polygons intersect with a linestring [duplicate]

sample image

import geopandas as gpd
parcels = gpd.read_file('parcels.shp')
roads = gpd.read_file('roads.shp')
intersections= gpd.sjoin(parcels, roads, how="left", op='intersects')
intersections.head()
    parcel                  geometry                         index_right  road
0  Parcel 1  POLYGON ((-0.6824583866837387 0.78233034571062...  0.0       Road 1  
1  Parcel 2  POLYGON ((-0.09859154929577452 0.3239436619718...  NaN       Nan
2  Parcel 3  POLYGON ((-0.9103713188220229 -0.1062740076824...  1.0       Road 2  
3  Parcel 4  POLYGON ((0.2266325224071704 0.620998719590268...  0.0       Road 1

With your solution

road = roads.unary_union
parcels['road_intersection'] = parcels.intersects(road)
parcels
    parcel                  geometry                         index_left  road_intersection  
0  Parcel 1  POLYGON ((-0.6824583866837387 0.78233034571062...   0         True 
1  Parcel 2  POLYGON ((-0.09859154929577452 0.3239436619718...   1         False
2  Parcel 3  POLYGON ((-0.9103713188220229 -0.1062740076824...   2         True
3  Parcel 4  POLYGON ((0.2266325224071704 0.620998719590268...   3         True
gene
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