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I am create geopandas DataFrames and create a buffer to be able to do spatial joins. I set the crs for the DataFrame and then proceed to create buffers and encounter the warning then.

df1 = gpd.GeoDataFrame(df1, geometry=gpd.points_from_xy(df1['Long'], df1['Lat']))
# set crs for buffer calculations
df1.geometry.set_crs('EPSG:4326', inplace=True)

df2 = gpd.GeoDataFrame(df2, geometry=gpd.points_from_xy(df2['Long'], df2['Lat']))
# set crs for buffer calculations
df2.geometry.set_crs('EPSG:4326', inplace=True)

# Returns a geoseries of geometries representing all points within a given distance
df1['geometry'] = df2.geometry.buffer(0.001)


/var/folders/d0/gnksqzwn2fn46fjgrkp6045c0000gn/T/ipykernel_5601/4150826928.py:10: UserWarning: Geometry is in a geographic CRS. Results from 'buffer' are likely incorrect. Use 'GeoSeries.to_crs()' to re-project geometries to a projected CRS before this operation.

  df1['geometry'] = df2.geometry.buffer(0.001)
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2 Answers 2

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You need to understand Geographic coordinate systems and Projected coordinate systems.

Geographic CRS(such as 'EPSG:4326') is not suitable for measuring distance. Converting degree to distance requires additional work. Use a different coordinate as the warning message shows. The coordinates you usually use depend on the area you want to analyze.It will be common to use a coordinate system based on UTM.

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  • We'll mostly be calculating distance within the United States.
    – kms
    May 1 at 16:58
  • And typically distance within 50m as we're looking for points in close proximity.
    – kms
    May 1 at 17:04
  • 2
    @kms I'm not sure what you mean. I'd like to recommend a specific coordinate system, but I don't know much about the United States. I searched and it seems that one of the coordinates of EPSG 26910 to 26919 can be used. Transform your coordinate system using gpd.GeoDataFrame.to_crs('EPSG:26910') and run the buffer.
    – Urban87
    May 2 at 0:42
  • Like what different coordinate system?
    – ifly6
    yesterday
2

Reproject your data to a coordinate system with meters as units using to_crs. Right now you are buffering with a distance of 0.001 degrees which means the distance will not be the same depending on where on earth you are.

df1 = gpd.GeoDataFrame(df1, geometry=gpd.points_from_xy(df1['Long'], df1['Lat']))
df1.geometry.set_crs('EPSG:4326', inplace=True)
df1['geometry'] = df1.geometry.to_crs("epsg:32633") #Change 32633 to a coordinate system which suits your data/requirements
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