Values for hillshade or slope are incorrect when using digital elevation model (DEM) in geographic projection

Last Published: April 25, 2020


When calculating slope, the output values for the resulting raster are incorrect. The values are usually much greater than expected.


When ArcGIS calculates a slope, or a hillshade, the x and y units (horizontal) are presumed to be the same as the z units (vertical). This causes problems because the linear distance of a degree of latitude varies.

Solution or Workaround

  • For data that must be maintained in a geographic coordinate system:

    Follow the steps in the ESRI Knowledge Base article listed in Related Information below.
  • For data does not need to be maintained in a geographic coordinate system:

    Project the data to a coordinate system that does not use decimal degrees or degrees minutes seconds for the x,y units of measure. Go to: ArcToolbox > Data Management Tools > Projections and Transformations > Raster > Project Raster.

Article ID:000008625

  • ArcMap

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