THE PLANE-TABLE AND ITS USE IN TOPOGRAPHICAL SURVEYING

This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1869 Excerpt: ...be given. Bluffs, if worn by the waves, will usually exhibit three slopes: 1 st, the caving slope at the top; 2d, the talus; 3d, the apron or flat, exposed wholly only at very low tides. The caving slope is sometimes perpendicular where tertiary country is being worn away--never where old dunes are yielding. The talus is usually of selected material--stones, perhaps. The talus and flat are generally wanting in bluffs worn by currents. As has been said, in no branch of surveying does so much depend upon skill, combined with good judgment and experience, as the faithful representation of hills over an extended and diversified area, and long practice and close observation only can give facility and accuracy in its execution. Various methods, more or less defective, in presenting a correct idea of elevations and depressions, have been contrived for topographical surveys; but the graphic representation of the successive gradations of level by means of horizontal lines, as at present employed in the Coast Survey, gives the nearest approximation to nature which has yet been devised, and when faithfully executed must Dtagrcuri illustrating the mode of constr%Lotlng Profile fromsPlcun Scale 10,000 Scale of Fro file, 10 of height to 1 of.Base. necessarily express very nearly, if not exactly, the shape and height desired. Contours, or horizontal curves, are the outlines of horizontal sections of ground at different elevations, with designated equal intervals between their planes, delineated in their true positions relatively to each other and the rest of the map, and agreeably to the scale of the map itself; or, briefly, a contour is the curve produced by the intersection of a horizontal plane with the surface of the ground. Perhaps contours may be described more simp...