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I'm passing an SRTM1 3601x3601 file to "gdaldem slope".....I've queried the values in Python, they are reasonable (min 222, max 424) for an area of SW Iowa. Took a bit to get the syntax right, but file is being created all right. Oddly though, almost all cells have a value from say 89.95 to 89.99, with a few having zeros (and the borders, no surprise / no problem, 9999). Looking at the 0's, it is when the elevation is flat, say for a water body.

Default slope is supposed to be degrees; anyone have any idea why I am getting the ~89.9x values?

  • sorry my imprecision if it is not clear; the 222-424 elevation values are from the raw SRTM1, and the odd 89.9X + several zeros values are in the gdaldem slope output file...... – Timbo1711 Apr 13 '17 at 15:55
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    It is because your horizontal units (X, Y) are decimal degrees and your vertical units are metres and you didn't use the -s scale in your gdaldem command. – user2856 Apr 13 '17 at 23:33

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