. Elements of military sketching and map reading . from each other (Fig. 22) ; , lines ofequal elevation. In other words, any point on anygiven contour has the same elevation above datumplane (usually taken at sea level) as all other pointson that contour. On the ground contours are, ofcourse, imaginary. Horizontal distances (ground distances) are meas-ured on a map by means of map scales, while thescale for contours is one for measuring vertical dis-tances betv\een adjacent contour planes. A simple demonstration of the theory of contouringis the following: Of a soft material (clay or wets
. Elements of military sketching and map reading . from each other (Fig. 22) ; , lines ofequal elevation. In other words, any point on anygiven contour has the same elevation above datumplane (usually taken at sea level) as all other pointson that contour. On the ground contours are, ofcourse, imaginary. Horizontal distances (ground distances) are meas-ured on a map by means of map scales, while thescale for contours is one for measuring vertical dis-tances betv\een adjacent contour planes. A simple demonstration of the theory of contouringis the following: Of a soft material (clay or wetsand) form a small irregular figure, giving It the shape 34 CONTOURS AND CONTOURING 35 of a hill. (Fig. 21.) Pass several horizontal planes(pasteboard) through this figure, carefully preservingan equal vertical interval between the planes. () Where a plane passes through the figure, bydrawing its shape with a pencil, an exact outline ofthe form of the ground at this particular level willbe obtained. (Fig. 23.) Cut each pasteboard along the. Fig. 21. pencil marks and file, as in Fig. 24. Press the paste-board to the bottom of the staff, and you have theway this hill would be represented on a map. (Fig. 25-) The picture of the same hill (Fig. 26) is shown asit would appear on a map by Fig. 26A. The horizontaldistance between contours, as from A to B (Fig. 26A),is called Map Distance (abbreviated M. D.) when thus 36 ELEMENTS OF MILITARY SKETCHING
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