I am using ArcMap to create aspect maps. I want to find the how many different directions the land faces (total aspect patch count) with continuous patches greater than three.

So for example I want to be able to say "this piece of land has 55 different slope faces while this piece of land has 60"

How do I do this?

  • Could you tell us how you define a "slope face"? – whuber Mar 15 '15 at 19:42

One approach could be this:

  1. Convert your aspect dataset to a polygon FeatureClass
  2. Union (1) with you land boundary dataset
  3. Select everything from (2) with an area greater than your desired threshold (I am assuming you meant 3 pixels)
  4. Run a summary statistics on the (3), group by land polygon ID, count as union polygon ID.
  • Hi hornbydd thanks for your answer but how do I convert a raster data set to a feature class? – tang Mar 14 '15 at 19:22
  • The 1st step is defining 'the same' aspect, because aspect raster is continious (thus can be converted to points only). This can be achieved by reclass. Output integer raster can be converted to polygons, etc following @Hornbydd solution – FelixIP Mar 14 '15 at 21:33

You can use the Region Group tool to find contiguous areas and the Lookup tool to filter by the count of contiguous cells.

Depending on the source of the original DEM, you may want to smooth it before calculating aspect as you'll likely get quite different answers depending on the level of noise in the original data (see this question).

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