Slope percent values,  0-489.53

844
2
Jump to solution
10-04-2013 08:56 AM
amyziegler
New Contributor
Hi, I am using a corporate data floating point grid for slope percent for my agency.  It is a floating point grid and the values range from 0-489.582.  I want to convert this to an integer grid, so that I may then convert to a polygon.  What I do not understand is the values...they seem too high to be an actual percent.  The cell size is 10m and the projection is NAD 83 UTM 10...I read another forum that if the values seem to high then perhaps it was because it needed to be converted to UTM first from degrees.  But this being corporate data, I do not believe the conversion was in error.  The rest of my organization is furloughed and I have no one to ask about this.
Thanks for any info....
0 Kudos
1 Solution

Accepted Solutions
EricRice
Esri Regular Contributor
Amy,

A 45 degree slope is a 100% slope.  If your terrain is rugged and/or contains vertical/near vertical cliffs you can easily get 400% slope.  Percent slope ranges from 0-Infinity.  The basic equation is Rise/Run *100.  So Rise 4, run 1 would return 400% slope.  Maybe the triangle graphics in How Slope Works will help you visualize.  You can see that a 76 degree slope equates to a 373% slope.  These graphics assume your X,Y,and Z all have the same units.  The only other thing that can cause weird slope values is when X and Y are in one unit (say meters) and your Z unit is in another (say feet).  If you saw % slope in the billions that would mean your XY is in decimal degrees (DD) and Y is in feet/meters.  You already said your XY is in UTM though so XY is not in DD.  I bet your data is just in a mountainous region.

Best,
Eric

View solution in original post

0 Kudos
2 Replies
EricRice
Esri Regular Contributor
Amy,

A 45 degree slope is a 100% slope.  If your terrain is rugged and/or contains vertical/near vertical cliffs you can easily get 400% slope.  Percent slope ranges from 0-Infinity.  The basic equation is Rise/Run *100.  So Rise 4, run 1 would return 400% slope.  Maybe the triangle graphics in How Slope Works will help you visualize.  You can see that a 76 degree slope equates to a 373% slope.  These graphics assume your X,Y,and Z all have the same units.  The only other thing that can cause weird slope values is when X and Y are in one unit (say meters) and your Z unit is in another (say feet).  If you saw % slope in the billions that would mean your XY is in decimal degrees (DD) and Y is in feet/meters.  You already said your XY is in UTM though so XY is not in DD.  I bet your data is just in a mountainous region.

Best,
Eric
0 Kudos
amyziegler
New Contributor
Yes, thank you, Eric, I finally realized that! Thanks so much for the response, though, it validated my thoughts on it.  I checked it out with the elevation and contours and it seems right on.
0 Kudos