I finally got the viewshed working correctly over one DEM model. However, I am wondering is it possible to do the viewshed over multiple DEMs? E.g. A Multiple County Viewshed based off one point.

The dataset source does not allow downloads over 2gb. So I'm forced to download each county separately. I think a vaguely remember a way to combine rasters. If that is possible, which tool do I use ?

  • Viewshed will only work on a single continuous raster (from a observer point located on the raster, not somewhere else), so you'll definitely need to mosaic it as Chris W describes.
    – Erica
    Jun 26, 2014 at 23:39
  • @Erica Is that entirely correct? I was under the impression you could also run it on a mosaic dataset, which is not actually a single contiguous raster though the tools treat it as such. I ask because I've not used that method myself. And I believe there is a distinction between a mosaic (which won't work) and a mosaic dataset (new at 10.0), as mentioned at this question.
    – Chris W
    Jun 26, 2014 at 23:55
  • I more meant to comment that it couldn't be run on multiple separate raster files, or with the point somewhere that's not on the DEM. If you mosaic them to a new raster, it works fine. I haven't tried running them on a mosaic dataset either.
    – Erica
    Jun 27, 2014 at 0:45

1 Answer 1


I believe you're looking for Mosaic to New Raster in the Raster toolset. It may take some fiddling depending on how well adjacent DEMs overlap/line up. If you're running into file download limits at 2GB, you may also end up running into a problem with your output raster being too large depending how many pieces you have to combine. This may require piecing fewer together at once, or possibly seeking a lower resolution DEM depending on how large an area you're trying to cover. Or just being very patient with processing times. :)

Another option would be to create a Mosaic dataset out of your individual rasters. This keeps the files separate rather than merging to one huge file, but the tool treats it as a single file. Relevant Esri Blog post.

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge that you have read and understand our privacy policy and code of conduct.

Not the answer you're looking for? Browse other questions tagged or ask your own question.