topic Slope calculation and coordinate system problem in ArcGIS Spatial Analyst Questions

Slope calculation and coordinate system problem

LukeMiner — Mon, 07 Feb 2011 09:41:56 GMT

I've got several elevation rasters in Mapinfo's tabbed grid format. I need to get them into ArcGIS, create rasters of the slope, and then average these values up by zone so I have a value of average slope per zone. My problem is that when I do this, I get values that make no sense. I think I have some problem with projections/coordinate systems.

The process I've gone through is as follows:
1. Open the mapinfo elevation raster in Global Mapper and export to DEM format
2. Run the DEM to Raster tool in ArcGIS without modifying the Z-value
3. Run the Slope tool from the Spatial Analyst toolset in ArcGIS to create a raster of the slope
4. Run Zonal Statistics as Table from the Spatial Analyst toolset

In terms of coordinate systems:
1. The original rasters are in WGS_1984_UTM_Zone_48N as is my dataframe.
2. I had to hand digitize my zones and they're in GCS_WGS_1984. I've tried reprojecting them to WGS_1984_UTM_Zone_48N with no apparent effect.

Am I doing something wrong here?

Re: Slope calculation and coordinate system problem

nicogis — Fri, 20 Apr 2012 07:20:45 GMT

FYI: http://blogs.esri.com/esri/arcgis/2012/04/17/grd-and-grc-files-now-supported-in-arcgis-10-1/

Re: Slope calculation and coordinate system problem

EricRice — Fri, 20 Apr 2012 14:35:32 GMT

Hi Luke,

It will be helpful to know what values your are getting. Your workflow is fine. Also, is it the slope values or the zonal results you are taking issue with? What is the Z unit of the DEM? Are you doing percent slope or degree? Look forward to hearing from you.

Eric