I totally need one of these

enter image description here

This helps you estimate the slope angle on a contour map by measureing the gaps between the contour lines. This is to help you avoid avoid avalanche areas.

I'm sure I could work this out but my maths is terrible. Anyone know what the mm gap is between each of the markers on this tool?

  • Could you be a bit more precise about "what the mm gap is between each of the markers on this tool"? I'm sure I could figure out the math, however, I don't understand from your question, what I'm supposed to figure out ;-) Feb 13, 2015 at 17:30
  • Which particular markers are you referring to?
    – user5592
    Feb 13, 2015 at 18:15
  • 5
    Keep in mind when you're measuring slope that the slope isn't always a "slope." I charted a slope for a summit attempt not long ago, but when we got to the mountain we discovered that our projected "slope" from the topographic map was actually a series of very steep steps 20-30m in height.
    – ShemSeger
    Feb 13, 2015 at 18:48

1 Answer 1


Image capture from John Balwin's website

Source: John Baldwin: Slope Angles from Map Contours

View this page for a refresher on how to do the maths to calculate slope on a topographic map.

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