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In ArcMap 10.1 I have reclassified several layers into 4 classes according to suitability. I have then run the Weighted Overlay tool, but the output does only have classes 1,2 and 3. Does anyone have an idea why that might be? What happened to my class 4?

I'll add a few pictures to make it a bit more visual. Here is (part of) my input in the Weighted Overlay tool: enter image description here

And this is my output. Notice how there are only classes 1 to 3, although my input rasters were classified into 1 to 4. Is this normal?

enter image description here

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It's perfectly reasonable that you wouldn't have the same range of values in your output. You may just not have any locations where the sum of the weighted values equals 4. I would recommend spot-checking locations where you expect high values across all or many of your inputs.

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  • Hi Tom, thanks so much for your answer. I am still a little confused by this. Can I assume that the classes 1, 2 and 3 are equal in meaning to my classes 1, 2 and 3? And that the weighted overlay concluded class 4 doesn't exist? In my context that would mean that none of the habitat is unsuitable for a certain animal species and I know that this can't be true.
    – Carina
    Commented Jun 13, 2016 at 16:57
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    @Carina, it depends. Are all the inputs on an interval scale? So, 4 represents unsuitable habitat in the input data? If so, then you must not have any single location that contains 4s across all of the input datasets. In which case, with a weighted overlay, no location would be 4. E.g., a location may have unsuitable slope, aspect, elevation, land cover, and precip, but if it has moderately suitable temperature, then--depending on your weights--it still wouldn't come out as a 4 in the output. If my interpretations are correct, there may be some methodological issues with this approach.
    – Tom
    Commented Jun 13, 2016 at 17:10
  • Okay, thanks very much again, that has really helped me a lot. I guess I will have to reditribute my weights so the animals don't come to live in the city. ;)
    – Carina
    Commented Jun 13, 2016 at 17:59
  • Or, after second thoughts, I should perhaps try to exclude the cities from the overlay calculation ... This is a bit difficult, since it's only a point layer. I will have to mull this over a little more ...
    – Carina
    Commented Jun 13, 2016 at 18:02
  • @Carina, if there are, e.g., certain land cover types that are 100% deal-breakers or strict elevation limits, then you may want to include a subsequent step in which those no-go zones are overwritten as unsuitable regardless of what comes out in the weighted overlay.
    – Tom
    Commented Jun 13, 2016 at 18:03

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