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Thread: Deriving Slope Percent vs Slope Degree

  1. #1
    Cadence Phillipe
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    Question Deriving Slope Percent vs Slope Degree

    Hi....question, when you use your DEM to create a slope raster, whats the highest possible value you can get if the slope is done in:
    1. Degree - I get up to 70 degree as the highest which seems ok but its the percent i'm interestd in
    2. Percent - FOR THIS I GET A VALUE OF ALMOST 300...is this possible? Isnt the highest 60? Plus the highest point in my country is just 2.2 km tall....would there be slopes over 60%. Why are my values like this?

  2. #2
    William Huber

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    Default Re: Deriving Slope Percent vs Slope Degree

    In degrees, horizontal is 0 and vertical is 90. All slopes lie between the two (and can include 0).

    In percent, the slope is expressed as 100*rise/run. These values can extend from 0 to arbitrarily large amounts. For example, a value of 300 corresponds to a rise of 3 meters for every 1 meter across: that's an angle of ArcTan(3) = 71.6 degrees. A 60% slope makes an angle of ArcTan(0.6) = 31 degrees.

    If your grid is detailed enough--say, 0.1 meter resolution--then even the sides of a small rock may result in slopes well over 100%. It doesn't matter whether the rock is at sea level or at 2.2 km altitude. A cliff can have slopes of 1000% or more.
    --Bill Huber
    Quantitative Decisions
    For more help, visit the worldwide community at http://gis.stackexchange.com

  3. #3
    Cadence Phillipe
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    Default Re: Deriving Slope Percent vs Slope Degree

    Thanks sooo much..this was indeed VERY informative

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