Creating slope map with ArcGIS Desktop?

Question

I created slope map with DEM model in ArcGIS Desktop. But it is only categorize in to two sections. I think it is problem with the horizontal and vertical scale. I used WGS84 coordinate system.

How do I overcome this problem?

Answer 1

Supply a z-factor in your slope tool parameters to convert your elevation units (I assume meters) to the horizontal coordinate units of your DEM (degrees).

From the documentation:

The z-factor is a conversion factor that adjusts the units of measure for the vertical (or elevation) units when they are different from the horizontal coordinate (x,y) units of the input surface. It is the number of ground x,y units in one surface z-unit. If the vertical units are not corrected to the horizontal units, the results of surface tools will not be correct.

Some roughly appropriate z-factors for particular latitudes are listed in the documentation (copied below) and for further info on calculating the z-factor yourself see this answer.

    Latitude    Z-factor
     0          0.00000898
    10          0.00000912
    20          0.00000956
    30          0.00001036
    40          0.00001171
    50          0.00001395
    60          0.00001792
    70          0.00002619
    80          0.00005156

Note that as the range of latitude in your raster data increases, the more approximate the results will be.