I am trying to perform the function join attributes by location as found on the QGIS menu Vector>Data Management Tools. I am seeking an open source python option for this. I know arcpy has a spatial join function but I'm trying to perform this outside of the ESRI environment.
2 Answers
You may want to take a look at Shapely and Fiona. Fiona is a wrapper for gdal to make spatial file import and export easy. Shapely provides geometry functionality. Here is a very simple example to give you the idea. It joins polygon attributes to all points within that polygon.
The example data I have used are these polygons and these points.
import fiona from shapely.geometry import shape from copy import deepcopy with fiona.open("planning_neighborhoods.shp", "r") as n: with fiona.open("Schools_Private_Pt.shp", "r") as s: # create a schema for the attributes outSchema = deepcopy(s.schema) outSchema['properties'].update(n.schema['properties']) with fiona.open ("Schools_withNbhd.shp", "w", s.driver, outSchema, s.crs) as output: for school in s: for neighborhood in n: # check if point is in polygon and set attribute if shape(school['geometry']).within(shape(neighborhood['geometry'])): school['properties']['neighborho'] = neighborhood['properties']['neighborho'] # write out output.write({ 'properties': school['properties'], 'geometry': school['geometry'] }) 
- Thanks @cengel. This looks like it will put me on the right track! I'm actually interested in the join with lines and polygons (specifically finding where rivers intersect model cells) and I think that will work following your example.mishaF– mishaF2013-10-28 15:26:54 +00:00Commented Oct 28, 2013 at 15:26
- @cengel Do qgis stations using plugins employing these methods require installation of modules and gdal?user25976– user259762014-05-05 22:36:36 +00:00Commented May 5, 2014 at 22:36
- @user25976 sorry, not sure I quite understand your question. My code example is a standalone python script. Both fiona and shapely require gdal.cengel– cengel2014-05-07 00:36:55 +00:00Commented May 7, 2014 at 0:36
- @cengel Excuse me, let me clarify (I'm new to programming). Regarding standalone python scripts: you mean that a plugin written with fiona and shapely imports can be used by QGIS users even if they don't have python or the modules installed on their computer?user25976– user259762014-05-07 00:47:21 +00:00Commented May 7, 2014 at 0:47
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Although still a bit rough around the edges, especially when it comes to documentation and examples, but geopandas' future looks bright. It basically combines the power of pandas dataframes with geospatial capabilities of shapely.
the function you look for is called sjoin
Make sure your machine/instance has enough memory to perform the operation
import geopandas as gpd import pandas as pd import os gdfLeft = gpd.read_file(os.path.join(PATH,INPUT_FILE_NAME_1)) gdfRight = gpd.read_file(os.path.join(PATH,INPUT_FILE_NAME_2)) gdfJoined = gpd.sjoin(gdfLeft, gdfRight, how="left", op='intersects') 
- This piece of code performs the spatial join but the attributes of the joined shapefile is empty. Any pointers?April– April2019-10-16 11:27:04 +00:00Commented Oct 16, 2019 at 11:27
Join attributes by locationcommand from thefToolsplugin:doSpatialJoin.py, particularly thecompute()method. Shouldn't be too hard to eliminate any UI code from that and strip it down to a plain python function.