I am trying to use the combine function on ArcGIS 10.3 for Desktop.

I have two raster files that have the same values and I want to combine them in order to compute an accuracy assessment through excel.

However whenever I compute the combine command I end up with a blank attribute table. I have checked to make sure they are in the same coordinate system, they are the same size, overlap, and have the same values to match up.

Does anyone know what the issue may be?

  • Check environment Extent, set it to intersect of inputs
    – FelixIP
    Apr 8, 2016 at 4:40

1 Answer 1


Please check if the two rasters are in integer values not floating and you can open their attribute tables. According to the ArcGIS help:

The Combine tool works on integer values and their associated attribute tables. If the values on the input are floating point, they will be automatically truncated, tested for uniqueness with the other input, and sent to the output attribute table.

Also select "ESRI GRID as output", because other formats may cause some problems, and make sure you don't select the names of raster images to begin with numbers.

  • Both rasters are long and double, so there are no floating points. I don't see on the combine function where to select "ESRI GRID as output". It just has inputs and then I can specify where to save my output?
    – PiRho
    Apr 9, 2016 at 13:05
  • Double means floating point. You need to convert you rasters to integer. When specifying the output without extension, it will be in ESRI GRID. please check the help here: help.arcgis.com/EN/ARCGISDESKTOP/10.0/HELP/index.html#//…
    – ahmadhanb
    Apr 9, 2016 at 15:09

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