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I have two shapefiles. One consists of squared grid cells and contains ... let's say precipitation data. The other one was downloaded from NaturalEarthData and contains country-internal administrative boundaries (e.g. states) ... as a mask layer. How can I add the average of the precipitation of all grid cells that are located within a mask polygon (e.g. a specific state)? Not only for one state but let's say I am actually covering the entire world.

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You can use rasterize tool to convert the grid vector into raster. In this tool you need to choose the attribute field that represents the precipitation and choose the x and y cell sizes that matches the grid x, y spacing. The tool is located in Processing toolbox -> GDAL/OGR tools -> Analysis -> Rasterize (vector to raster) tool

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Then use Zonal statistics to calculate the mean (average) of raster precipitation within the polygon.

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The above workflow is for QGIS 2.14 and 2.18 and probably QGIS 3.0 (still not yet downloded).

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  • Thank you for your response. I'll check it out and get back to you
    – Stücke
    Mar 8, 2018 at 12:31

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