Problem of slope average in crest zone

[YannickCREST]

Hi everybody!

I delimited catchments on raster map of the Pyrenees, constructed from LiDAR data.

I want to obtain slope average of these catchments. So I use 3D Analyst tool to add Z information.

The average slope is higher than 90° and is even higher than 500° for some catchments.

This problem is derived from the Z data of the crest zone, probably because of the steepness of these crests.

Does someone know how to resolve this problem and to obtain more "classical" average slope?

PS: when I contruct slope map from the raster, there is no problem and all the slope values are between 0° and 90°, even in the crest zone...

[DanPatterson_Retired · Accepted solution]

You didn't set it to calculate slope in degrees but in percent

[YannickCREST]

How is it possible to set it in degrees using "3D Analyst tool Add Z information"?

[DanPatterson_Retired]

by the wildest chance are your coordinates in decimal degrees and your z values in meters?

[YannickCREST]

I don't know. Where can I find these informations?

It's a raster from the spanish IGN

In the layer properties menu, we can read:

"Spatial reference : ETRS 1989 UTM Zone 31N"

"Linear unit : meter (1.00000)"

"Angular unit : degrees (0.174...)"