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I have two raster datasets. One raster dataset shows population density, with the range of population density values given a score from 1 to 10. The score is entered into a separate column.

The second raster dataset is average income. The range of average income values have been given a score from 1 to 10. The score is entered into a separate column.

I would like to integrate these two raster datasets and create a third. I would like the third raster dataset to display the sum of the first two raster dataset scores. So the third raster dataset will have values ranging from 2 to 20.

I am using ArcMap 10.3 with the spatial analyst extension.

Edit: The context is conservation planning. We have a number of layers that we would like to integrate to develop an overall "cost score". The individual input layers have been scored so that a value of 10 indicates highly modified or impacted / not worth protecting. A lower score indicates the opposite. This will feed into a larger analysis involving species' distribution, endemicity, etc.

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    Not sure what the end game is here but summing these rasters may not be the best option. Say a cell had a value of 11, how would you know if it was low density high income, high income low density, or any other combination? – landocalrissian Oct 7 '16 at 14:56
  • Hi Chris. The context is conservation planning. We have a number of layers that we would like to integrate to develop an overall "cost score". The individual input layers have been scored so that a value of 10 indicates highly modified or impacted / not worth protecting. A lower score indicates the opposite. This will feed into a larger analysis involving species' distribution, endemicity, etc. – Thomas King Oct 10 '16 at 14:29
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If you're using ArcGIS Desktop, Cell Statistics sounds like it could do the job (using the "SUM" statistic type).

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If you use the ArcGIS combine tool the result will be an integer raster with a raster attribute table (RAT) containing new unique raster value representing all of the value combinations with additional columns for each source rasters original value(s).

Then, if you wanted the sum you could just sum the two original raster value columns to create a new column. If you really are just after the sum of the the two rasters just use the raster calculator with a syntax of [r1] + [2] but please heed @Chris R's warning that by summing you do not know the resulting relationship because this does not appear to be a cumulative process.

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I think there are two tools that can help you accomplish that:

  1. Cell Statistics (Use Sum)
  2. Raster Calculator. This is the method I prefer under these circumstances. You can just add them up
  • Hi Andrew. Thank you for your input. I am having trouble with the fact that my individual raster layers have attribute tables with a number of columns. When I run the Cell Statistics tool, and do a simple "Sum" calculation, it does not sum the values in the columns that I desire it to sum. There does not appear to be an option in the tool that allows me to specify the specific columns in the individual rasters that I want it to sum. I'm a novice user of rasters. I'd be grateful for your advice and input. – Thomas King Oct 11 '16 at 8:49
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    Have you tried turned these irrelevant fields off while doing Raster Calculator? If these columns are not pertinent to your result, you can even delete them. Let me know how it works – AndrewLebron Oct 11 '16 at 12:53
  • It worked! Just turning the fields off was sufficient, I didn't need to delete them. Thanks for all your help. – Thomas King Oct 12 '16 at 9:29
  • Ok I have selected all your answers as being useful. I hope that is the same thing. Not sure how to "accept". Let me know if there is something I still need to do. – Thomas King Oct 16 '16 at 9:38
  • Update on use of Raster Calculator: I found that, with some rasters, turning off the fields that were unnecessary for the raster calculation didn't prevent them being included in equations. I realised that the three important columns in a raster are the OID, VALUE and COUNT fields and that the raster calculator only works with the value in the VALUE field. I may be wrong, but it doesn't seem as though you can run equations on other fields in the raster. I used the "Lookup" tool to export the field of interest as a new raster, to use in calculations. – Thomas King Oct 25 '16 at 7:21

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