Practical GIS

Spatial joins

Like queries, we can also perform joins based on the location of the target and reference features. For this task, we need geometries in both the layers. This is a very handy operation when there are no common columns for joining and making one would require excessive work. To avoid ambiguity, we must have a spatial relationship able to do a one-on-one mapping between features. If not, QGIS will either pick the first matching feature or attempt to calculate statistics from the multiple target candidates.

Let's have an example, say, we would like to fill our administrative boundaries layer with population data. Our GeoNames layer has this kind of data, but they do not have a common column. If we join the whole GeoNames layer ...