I try my best to explain my problem in english:
We use QGIS. We have a shapefile that shows a city divided in 277 areas. We have computed the centroids of each of these areas. Next step we have georeferenced adresses of general practitioners. Then we made a buffer around each general practitioners.
Now we'd like to have a new column in our attribute table that shows, for each area centroid, by how many buffers it is covered. We have tried to solve it with the field calculator to use "sum" without success.