Topographic surveying; including geographic, exploratory, and military mapping, with hints on camping, emergency surgery, and photography . churenear the extremities or by interpolating short lines betweenthe original hachures. Hachures are made shorter and widerfor steep slopes, and are lenghtened and narrowed as the in-clination decreases. CONVENTIONAL SIGNS 463 The first principle upon which hachures are constructed isthat the steeper the slope the less light is received in the in-verse ratio of its length. Various methods of expressing thedegree of shade, or the ratio of black to zuhitc, h
Topographic surveying; including geographic, exploratory, and military mapping, with hints on camping, emergency surgery, and photography . churenear the extremities or by interpolating short lines betweenthe original hachures. Hachures are made shorter and widerfor steep slopes, and are lenghtened and narrowed as the in-clination decreases. CONVENTIONAL SIGNS 463 The first principle upon which hachures are constructed isthat the steeper the slope the less light is received in the in-verse ratio of its length. Various methods of expressing thedegree of shade, or the ratio of black to zuhitc, have beenadopted by various draftsmen. The Enthoffer or Americanmethod is to indicate the degree of slope by varying the dis-tance between the hachure lines, the distance between thecenters of lines to be .02 of an inch plus one-fourth of thedenominator of the fraction denoting the declivity, expressedin hundredths of an inch. The lines are accordingly madeheavier as the slope is steeper, and finer for gentle slopes, in-creasing in width until the blank spaces between them equalone-half the breadth of the lines. (Fig. 142.) The German. Fig. 142.—Shaded Hachures. or Lehmanns method consists in using nine widths of linesfor slopes from zero to 45°, the first being white and the lastblack. For the intermediate slopes the proportion of whiteto black is as 45° minus the angle of slope is to the angleof slope. Steeper slopes than 45° are represented by short,heavy lines, parallel to the contour lines. 195. Conventional Signs.—Various conventional signsare employed in topographic drafting to represent roads,houses, woods, marshes, the shapes of hills, etc. Thesesigns may be divided into three general classes : I. Signs to represent culture or the works of man. 4^4 TOPOGRAPHIC DRAWING. 2. Signs to represent hydrography or water. 3. Signs to represent hypsography or rehef. In the making of a geographic map or of a topographicmap for the use of a government or State, only such cult
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