Slope Calculation Problem

[KenBerglund]

Hello,

I am having problems simply calculating % slope from a USGSDEM. Even though it had a GCS_North_American_1983 projection, I defined its projection to be that as well after reading some posts on the same issue. The resultant slopes have values into the millions. I then tried to project the DEM into UTM to ensure the units would be in meters. This caused an error. Under the spatial reference in the DEM, the "Linear Units" are blank. This is why I think the project to UTM failed as it does not have linear units defined. Anyone have any ideas? This should have been a simple task but has been troublesome. I guess I am asking, why would the slope % be in the millions? Or any ideas on why the project to UTM failed? Or how to define linear units?

Thanks for any help

Ken

[blairstuart]

Hello,

I realize that this is an �??old strand�?� �?? maybe even ancient (two years!) �?? but in case if anyone�??s still listening:  With respect to the Slope Tool in ArcGIS 10.1, I�??ve tried the fix that Randy discovered and it hasn�??t worked for me.

That is, (i) my raster data is projected and has linear units (USGSDEMS having spatial reference:  NAD_1983_UTMzone_14N,  Linear Unit: meter (1.0), Angular Unit: degree (.0174), Datum: North_Am_1983),  (ii) the z and  x,y units are the same; and (iii) I applied the �??bilinear interpolation�?� resampling option --  BUT I�??m still getting wonky slope values, i.e., the smallest range category is 0 �?? 319,000 or so. Is it possible that degrees are still being used in the algorithm for some reason?  Also, �??resampling during display�?� seems to have no effect �?? might there be something I�??m not doing and should be doing?

By-the-by, does anyone know why using an Output Measurement of �??Per Cent Rise�?� at least result in a recognizably correct image, whereas using �??Degree�?� does not, at least not for me

Thanks for any help that anyone has time to give.
Blair S.