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 '14 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 '14 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 '14 at 0:45

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.

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