Elevation Mask

clip_image001[1]How to quickly mask a region based on elevation values without creating additional files to manage and store.

Every year soon after the snow flies the department conducts aerial moose surveys. Flight time is expensive, so to focus efforts they skip areas that aren’t habitable. At right is a sample of what they’ll take with them, depicting the survey grid and “don’t bother” zones in transparent red.

A crude but effective means is to ignore everything above 5,000’ (1524m) elevation. The quickest and easiest method is to use Symbology to classify the DEM into less than and greater than the split value, and overlay it on top of the relief map.

 

  1. Load DEM >> Properties >> Symbology >> Classified
    1. Change Classes to “2” >>  [Classify…]
    2. Set 1st break to 1525 (DEM is in meters) and 2nd to highest possible, 6,000 for YT
  2. Change symbol colours: 2x-click on patch area >> then
    1. 0 – 1525 to transparent (No Colour)
    2. 1525 – 6000 (whatever)
  3. DEM Layer Properties >> Display >> set transparency as you like

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Optional: Export classification mask

If you want to use the mask for analysis Layer >> Data >> Export >> “Use Renderer” will create a raster using your classes instead of the elevation values.

 

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