Joining multiple polygons inside a single polygon in QGIS

Question

I need to somehow "join" information from two shape files:

1. zoning - these are large polygons indicating the zoning code for a moderately large area, typically hundreds of separately owned parcels (see #2) are fully contained in each. The boundary files of zoning seem pretty "rough hand drawn", with boundaries typically running down the MIDDLE of the streets. They are however completely closed and do not overlap.

2. parcels - these are relatively small polygons, with precise lot boundaries, one for each separately owned parcel. None of these polygons extend out into the street. Related to each parcel id is a lot of useful tabular data, however.... that data doesn't include the actual zoning code (eg residential, commercial, industrial, office/residential, etc, etc, etc.) Ideally I'd like to just "compute" or "look that up" from the more aggregate zoning shapefiles and add a column to the parcels tabular data (unless of course there is a better way...)

Totally new to vector->geo processing tools->

Gave Union a quick whirl but got odd results, long processing time, and a very large output file, perhaps due to the fact the darn zone file borders run down the center of the street vs. the strict property boundaries contained in the parcels file.

Answer 1

Assuming the screenshot of my interpretation of your data is correct - you could try the following:
1) Select menu Vector>Data Management Tools>Join attribute values by location:

Result: - New poly dataset same as parcels but with additional field(s) from zones. Labels here include both id fields from parcels and zones.