qgis
I'm trying to count the number of polygons in a multipart feature. My aim is to have a 'count' attribute to quantify fragmentation of multipart land parcels.
I've looked at the field calculator and for suitable plugins, but can't see anything that would help. There are lots of ways to count points, lines and vertices, but not polygons.
Number of points - just simple formula in QGIS field calculator:
num_points($geometry)
See the screenshot below: in this case, the number of vertices of each feature is added to the field "vertex" in the attribute table. Alternatively, you can create also "Create a new field" and get results there.
I couldn't find the field count in the fTools anymore (QGIS 2.0). But I managed to get the number of lines within a polygon using the plugin MMQGIS. Assuming you have a line layer test.shp and a polygonlayer buffers.shp you have to do the following:
Choose MMQGIS > Combine > Spatial Join
Select the parameters:
Output Shape (Target) Layer: buffer.shp
Spatial Operation: Intersects
Data (Join) Layer: test.shp
Attribute Operation: First
Output File: example.shp
The output file example.shp contains the attribute count, which gives you the number of lines within each polygon.
Best Answer
4 years later it seems as if QGIS has integrated this feature into the field calculator. The expression syntax is:
num_geometries($geometry)