1Geography 12: Maps and Spatial ReasoningLecture 14:Representing heights on maps Professor Keith ClarkeContours on maps. What CI?What is a contour line?•Imaginary line joining points of equal elevation above or below a datum•Contour lines have a specific contour interval•Interval is the vertical distance between contours•CI is a function of scale and units•Relief is the highest elevation shown minus the lowestContour lines
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2Features of contours•Contour interval•Index contours•Intermediate contours•Supplementary contours• Depressions•Uncertain contours•Bathymetry: isobathsContour interpretationInterpolation100xCI=20mYZX > 140 and < 160Y > 120 and < 140Z > 100 and < 120SlopeSlope = Rise vs. RunFour expressions:•Slope ratio (e.g. 1:10)•Slope fraction (e.g. 1/10)•Percent slope (rise per 100 units of run) 10%•Degrees from horizontal (tan S = rise / run)