[Qgis-user] Aggregation of polygons into vector grid

[Sebastian Schubert]

Hi,

I have a map with several polygons i, each having a certain value x_i. I 
want to calculate the average value of x in a rectangular grid. Each 
cell j of this grid includes (parts of) several polygons with A_ij being 
the area of the part of polygon i being in grid cell j. With that the 
average value in grid cell j is

x_j = sum_i A_ij x_i / (sum_i A_ij)

I was able to create a grid with Vector > Research Tools > Vector grid. 
Now each cell of this grid should include the average value of all 
polygons inside the cell (as described above).

Any idea how to do that?

Thanks a lot!
Sebastian
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