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I have several presence maps (rasters values 1 and 0) from different species. They are all from South America, but they do not have the same extend (i.e., different sizes).

So, I am trying to develop a "richness" map, trying to sum all these values, which would give me a value of the number of species for each pixel (from 1 to 6, as they are six species).

However, when trying to use the raster calculator and other grid analysis tools, this fails because: 1) it shows me only a map with areas where they all overlap (this happens with raster calculator), or 2) fails because the layers are different (different extent, this happens with grid sum, and other analysis tools).

How can I have a map that sums all pixels values, and includes the areas of all the different presence maps?

  • What about resampling all rasters to the same extents and resolution? – Zoltan Feb 27 '16 at 6:07
  • What do you mean "presence maps"? – whyzar Feb 27 '16 at 20:21
  • I guess I could resample all rasters to the same extend.... but I was looking for a way not to need that, and just use the maps I have... – Fran Astorga Feb 29 '16 at 13:26
  • Concerning the question, a "presence map" is a map were I assume that the species could be present, according to the outcome of the niche modeling and a threshold defined with previous methods (many papers of Townsend Peterson). – Fran Astorga Feb 29 '16 at 13:27
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You should use the r.series tool from the GRASS commands in the processing toolbox tools.

Here's an example of 3 rasters with 0, 1 data, and their differing extents enter image description here

The r.series tool lets you choose the algebraic operation, in this case SUM

enter image description here

And the result is 1 raster with a conjoined extent, with values ranging from 0 to 3 (well, in this case only 2 as I didn't have a pixel shared by all 3)

enter image description here

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