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I have 5x5km grid rasters of monthly average wind speed for the UK. I want to convert these into yearly averages, what is the best way of doing so?

The only way I'm aware of is to polygonise the 12 rasters and export geometry/attribute data through mmqgis but that generates point data rather than polygon data. I've read in this which might do the trick: Converting point sets to polygon boundaries?

Is there a better/more efficient way around this?

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You can use the GRASS r.series tool in processing toolbox to calculate per-cell average (as well as other statistics) for chosen raster layers.

There really is no need to polygonize you raster data for this calculation.

This is the processing toolbox window, it appears under the raster group in the GRASS provider. enter image description here

In the tool, you choose layers from file or from the layer menu (5 raster layers in this case), select the function (average), and the default result is one taster with the same extent and resolution as input layers.

enter image description here

  • Sorry but this would be my first time opening GRASS and the article you linked makes very little sense to me. Could you elaborate just a touch? – James B Apr 26 '17 at 12:52
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    For anyone on QGIS >=3 but <3.7 reading this, careful with this bug: issues.qgis.org/issues/21452 You will get empty or 0 results if you don't manually set the ranges. – bugmenot123 May 1 at 9:15

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