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I'm adding two rasters that have different extent. The result is a raster with the extent of the smaller one, which is not what I want. What do I need to do to have the output raster as big as the biggest of the input rasters? I have tried to increase the extent of the smaller one with "Copy Raster" and in 'Environments' I have selected the biggest raster as 'Extent' and 'Snap Raster'. This has not worked unfortunately.

Am I doing anything wrong? Is there any other way to do what I'm trying to do?

NOTE: I need to extend the smaller raster and set all those new cells to 0.

  • Just to clarify, does the smaller raster always fall entirely within the larger raster? – Hornbydd Dec 13 '17 at 17:56
  • Yes, it does fall entirely within the larger raster. – Pitrako Junior Dec 13 '17 at 20:17
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One approach is this:

  • Reclassify all the cells in your larger raster to zero using the reclassify tool.
  • Add your smaller raster to your new large zero raster using the Plus tool.
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    The first step was only to set up the background of zero values that the OP was looking for. – Hornbydd Dec 14 '17 at 9:09
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The problem is likely to come from the presence of nodata values, which "absorb" other values in a computation. In you case, you could use the raster calculator (geoprocessing > toolbox > spatial analyst > map algebra), define the output extent as the union of the inputs, and then apply :

Con(IsNull("your_small_raster"), "large_raster", "large_raster" + "your_small_raster")

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