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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so deep for the high areas that it obscuresthe lettering and conventional signs. A sheet showing aportion of the top of a high plateau with low relief wouldbe colored a deep brown or magenta all over, and no em-phasis would be possible to assist in picturing such relief asdoes exist.* The so-called oroscopic system, which is also based onthe layer relief model idea, is illustrated in Fig. 17. Thesystem in the form shown, which is taken from Morrows * See some of the English maps of South Africa. 34 WHAT A TOPOGRAPHIC MAP SHOWS Contours and Maps, * is applicable only to relief maps asthe deep base tint obscures conventional signs. The schemeis based on layers with horizontal lighting at 45 degrees fromthe upper left-hand corner. The edges of those layers whichare toward the light are shown white, while the edges awayfrom the light are drawn in black. The system is quite astriking one and can be worked out without a ground tintby using two colors for the contour lines themselves, say a
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Fig. 17.—Oroscopic System for Contour Maps. light pink and deep red. No maps are made in this way, butit is suggested as an advantageous modification of the typeshown. Various methods of shading have also been used in connec-tion with contour maps and these probably offer one of themost satisfactory solutions of the problem. The Norwegianmaps use shading which is sometimes referred to as based ona vertical lighting system. It is simply the substitution ofshading for hachures. Thus on the English Ordnance maps, * See Appendix. CONTOUR AIDS 35 where hachures and contours are used, the hachure may besaid to be line shading based on the principle that the steeperthe slope the darker the shading. On the Norwegian mapsthe shading is produced not by lines but by a gray tint ofvarying intensity. The effect is the same as if the groundwere lighted from directly above, the steep slopes which wouldreflect little light being dark, the gentler slopes lightly shadedand flat mountain tops or plain

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