topic Re: How do I derive slope from a very large DEM? in ArcGIS Spatial Analyst Questions

How do I derive slope from a very large DEM?

Anonymous User — Wed, 29 Apr 2020 19:48:33 GMT

Hi there,

I'm trying to calculate slope based from a national DEM - USGS 3D Elevation Program (3DEP), found here: 3DEPElevation (ImageServer) - and am having trouble with the spatial analyst geoprocessing tool given the size of the raster. When I try calculating slope in ArcMap Desktop, I get an error message saying that the file is too large. When I use ArcGIS Pro, it processes up to 5% and then stops. I'm using a VM, so bandwidth is not the issue. Does anyone have any tips on processing national DEMs? Or are there any pre-processed national slope files out there that I could download?

Thanks!

Re: How do I derive slope from a very large DEM?

JoeBorgione — Wed, 29 Apr 2020 20:10:18 GMT

I ran into the same sort of problem recently trying to process just one county worth of imagery. I cannot imagine the cpu and and memory (and probably graphics memory too) to complete a full country. Is there a way you can get the data into manageable chunks?

Re: How do I derive slope from a very large DEM?

Anonymous User — Wed, 29 Apr 2020 20:40:29 GMT

All of the other DEMs that I've found are at county-level or similar, which would be a hassle to patch together at the end. Unfortunately, I need a national slope raster to conduct analyses!

Re: How do I derive slope from a very large DEM?

DanPatterson_Retired — Wed, 29 Apr 2020 21:51:31 GMT

The page you posted suggests you can download the slope map itself, rather than calculating it.

Re: How do I derive slope from a very large DEM?

JoeBorgione — Wed, 29 Apr 2020 22:06:04 GMT

I just added the url to an arc pro session: not sure how to get the slope data out of it though...

I think I see where Dan lives....

Re: How do I derive slope from a very large DEM?

curtvprice — Sat, 02 May 2020 23:16:39 GMT

Are you sure you need full resolution on this? Bandwidth may not be an issue, but processing zillions of cells with any neighborhood operator is just a LOT of data to process. Even if you downloaded tiles on the data it would take you weeks I'm sure.