Figure 8-15.-Control-point method of locating contour.Figure 8-16.-Sketching contours by interpolation betweencontrol points of known elevations.elevation changes radically), you can draw a contourmap of the area by interpolating the desired contoursbetween the control points.A very elementary application of the method isshown in figure 8-15. Point A is the summit of a moreor less conical hill. A spot elevation is taken here. Spotelevations are also taken at points B, C, D, E, and F,8-15Figure 8-17.-Cross profiles.which are points at the foot of the hill. It is desired todraw the 340.0-foot contour. Point a on the contour lineis interpolated on the line from A to B, point b isinterpolated on the line from A to C, point c isinterpolated on the line from A to D, and soon.Figure 8-16 shows a more complicated example inwhich contours are interpolated and sketched betweencontrolling spot elevations taken along a stream.Cross RefilesIn the cross-profile system, elevations are takenalong selected lines that are at right angles to a traverseline. Shots are taken at regular intervals or at breaks orboth in the ground slope. The method is illustrated infigure 8-17. The line AB is a traverse along which100-foot stations are shown. On each of the dottedcross-section lines, contours are located. The particularcontour located at a particular station depends on (1) theground elevations and (2) the specified contour interval.In this instance, it is 2 feet. The method used to locatethe contours is the one described earlier for tracing acontour system. When the even-numbered 2-footinterval contours are located on all the cross-profileslines, the contour lines are drawn through the points ofequal elevation.
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