mlaloux · April 12, 2013 14:17 · Apr 12, 2013
diff --git a/How to add a column in QGIS.py b/How to add a column in QGIS.py
@@ -0,0 +1,36 @@
+If you want to use Python, you don't need QGIS, except if you want to create a plugin. In this case, you should consider PyQGIS with the reference given by Curlew
+
+But you can also use Python modules like pyshp, osgeo (gdal and ogr) or Fiona and Shapely without QGIS
+
+In both cases, you need a join field that will link the polygon shapefile to the point shapefile.
+
+Example with Fiona and Shapely (all the elements of a shapefile (schema,geometry, records) are processed using Python dictionaries).
+
+With ogr and Fiona it is easier to create a new shapefile, copying the original shapefile (geometry and attributes), and adding new fields with the desired values than modify the original shapefile.
+
+from shapely.geometry import mapping
+import fiona
+# open the polygon shapefile
+with fiona.collection('polygon.shp', 'r') as polygon:
+    # copy of the schema of the original polygon shapefile to the output shapefile (copy)
+    schema = polygon.schema.copy()
+    # creation of the new field color in the new schema
+    schema['properties']['color'] = 'str' 
+        # output shapefile with the new schema
+        with fiona.collection('join_poly_pt.shp', 'w', 'ESRI Shapefile', schema) as output:
+            # open the point shapefile with colors
+            with fiona.collection('point.shp', 'r') as points:
+                 polygons = [elem for elem in polygon]
+                 points = [elem for elem in point]
+                 # joint
+                 for poly in polygons:
+                     for pt in points:
+                         # common field for the join
+                         if poly['properties']['test'] == pt['properties']['test']:
+                             # construction of the new shapefile
+                             res = {}                  
+                             res['properties'] = poly['properties'] 
+                             res['properties']['color'] = pt['properties']['color'] 
+                             # geometry of of the original polygon shapefile
+                             res['geometry'] = mapping(shape(poly['geometry']))
+                             output.write(res)