 HOW TO

# Create a hillshade or slope using data in Geographic coordinates

Last Published: April 25, 2020

## Summary

When performing a hillshade or slope function in ArcGIS, the Z units are presumed to be the same as the horizontal (x,y) units. When working with data in geographic coordinates, this is a problem because the linear distance of a degree of latitude varies. In some cases, a value of 0.000003 was suggested as the Z factor to account for the actual Z unit in meters. While that value can still be used, this article presents a more accurate method of determining the Z factor when the Z units are in meters.

## Procedure

The following procedure assumes the Z units of the raster being used to generate the hillshade or slope are meters. If the Z units of the data being used are feet, first use the raster calculator to multiply the raster by the conversion factor 0.3048, so that the z units are meters.

1. Determine what the middle latitude of the area of interest is.
2. Convert that degree value to radians.
3. Use the value in radians in the following equation:
Z factor = 1.0 / (113200 * cos(<input latitude in radians>))
4. Use this calculated Z factor in the hillshade or slope tool.

Article ID:000007956

Software:
• ArcMap
• Legacy Products

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