How To: Calculate the average slope of an area using contour lines


Instructions provided describe the steps for calculating slope using contour lines, and then finding the average, or mean, slope for an area.

Spatial Analyst is required to complete this process


  1. Convert the contours to a surface using the Topo to Raster tool, found in the Interpolation Toolset in either 3D Analyst or Spatial Analyst toolbox.
  2. Calculate the slope using the surface created in step 1 as the input.
  3. Run Zonal Statistics from either the Spatial Analyst toolbar, or the Spatial Analyst toolbox > Zonal toolset.
    A. Specify the Zone layer.
    B. Use the output from step 2 as the Value raster.
    C. Either check Join output table to zone layer for All statistics, including Mean, to be added to the raster parcels dataset, or if the tool is run by way of the Zonal toolset, specify Mean as the statistic to be calculated.

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