File:Topographic maps and sketch mapping (1920) (14779231625).jpg

Identifier: topographicmapss00finc (find matches)
Title: Topographic maps and sketch mapping
Year: 1920 (1920s)
Authors: Finch, James Kip, 1883-
Subjects: Cartography Military maps
Publisher: New York : John Wiley & Sons, Inc.
Contributing Library: The Library of Congress
Digitizing Sponsor: The Library of Congress

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ed figures of irregular shape and in many cases they donot close at all but pass off the edges of the map. These lineson the map represent imaginary lines on the ground thatpossess this peculiarity, namely, they join points which allhave the same elevation. When we find a contour line num-bered 1000 this means, therefore, that every point on this * This refers to the scale of the map which is discussed in Art. 10. 20 WHAT A TOPOGRAPHIC MAP SHOWS line is just 1000 feet or meters, as the case may be, above thezero level, which is usually the level oi the sea. Contoursare sometimes described as successive shore lines and it istrue that the zero contour will be a shore line and that if weimagine the level of the sea to be raised 1000 feet the newshore line will be the 1000-foot contour and similarly for othercontours. It is clear, therefore, that a man walking along theside of a hill and always staying at the same level, goingneither up nor down, will be tracing out a contour line. (a) _^
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Fig. 8.—Showing Principles of Contours. Some of the fundamental characteristics of contourscan be shown by the experiment illustrated in Fig. 8. (a) Shows a perspective view of a box the front of whichis glass and in which there are placed three solids as shown,a right cone, a slanting cone and a hemisphere. The bottomof the box is assumed to be sea level, the zero level. Wateris put in the box so as to fill it to a depth of 10 feet and thenew shore lines on the solids are drawn and marked 10.Another 10 feet of water is then put in giving a total depthof 20 feet and resulting in the shore lines marked 20. Thisprocedure is followed until the solids are all submerged. Ifwe look down on the tank from directly above, the successive PRINCIPLES OF CONTOURS 21 shore lines on the solids will look as shown in (6). The threeseries of curves in (6) are therefore the contours of the threesolids and the numbers on these contours indicate the heightof the contours or shore lines above the zero le

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