Figure 8-19.-Uniform, gentle slope.Figure 8-21.-Concave slope.that appears on the map completely closed may indicateeither a summit or a depression. If the line indicates adepression, this fact is sometimes shown by a successionof short hachure lines, drawn perpendicular to the innerside of the line. An example of a depression is shown infigure 8-18. A contour line marked in this fashion iscalled a depression contour.On a horizontal or level plane surface, the elevationof all points on the surface is the same. Therefore, sincedifferent contour lines indicate different elevations,there can be no contour lines on a level surface. On aninclined plane surface, contour lines at a given equalinterval will be straight, parallel to each other, andequidistant.A number of typical contour formations are shownin figure 8-18. For purposes of simplification, horizontalscales are not shown; however, you can see that variousintervals are represented. The arrows shown indicate thedirection of slope.Generally, the spacing of the contour lines indicatesthe nature of the slope. Contour lines (fig. 8-19) that areevenly spaced and wide apart indicate a uniform, gentleslope. Contour lines (fig. 8-20) that are evenly spacedand close together indicate a uniform, steep slope. Thecloser the contour lines are to each other, the steeper theFigure 8-20.-Unifrom, steep slope.slope. Contour lines closely spaced at the top and widelyspaced at the bottom indicate a concave slope (fig. 8-21).8-17
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