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I have a shapefile with the geographical boundaries of towns in a specific region; then i have a csv file (with xy coords) with a lot of measurements about pollution in this region.

I'd like to have the mean value of pollution for town, obviously averaging over the measurements inside each town. How can i do it? I'm new to QGIS.

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  1. Load in your city boundary shape via the QGIS "add vector layer" symbol
  2. Active the "Add delimited layer" plugin in QGIS (or use the extension mmqgis)
  3. Load in your pollution file (the one with xy coords) via the previously activated plugins
  4. Check that both files have the same spatial reference (Rightclick on Layer -> save as with your project CRS). Then load in both reprojected files
  5. Go to "Data management tools" in the vector menu. Click "join attributes by location".
  6. Export the resulting attribute table via the mmqgis "export attributes" function.
  7. Process your table in R, LibreOffice or whatever you're used to
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"join attributes by location" should enable you to get the mean. I think, there might be no need to export anymore. –  underdark Nov 16 '12 at 21:04
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