. The elements of railroad engineering . f the grade at Station 71 ? Solution.—To obtain the elevation of the grade at Station 71, weadd to the elevation of the grade at Station 20, 140 feet, the total risein grade between Stations 20 and 71. Accordingly, 71 — 20 = 51; .75foot X 51 = feet; 140 + = feet, the elevation of gradeat Station 71. SURVEYING. G73 TOPOGRAPHICAL 292. General Definition.—Topographical sur-veying is the location and representation of the inequalitiesof any portion of the earths surface. The portion surveyedis conceived to be projected upon a
. The elements of railroad engineering . f the grade at Station 71 ? Solution.—To obtain the elevation of the grade at Station 71, weadd to the elevation of the grade at Station 20, 140 feet, the total risein grade between Stations 20 and 71. Accordingly, 71 — 20 = 51; .75foot X 51 = feet; 140 + = feet, the elevation of gradeat Station 71. SURVEYING. G73 TOPOGRAPHICAL 292. General Definition.—Topographical sur-veying is the location and representation of the inequalitiesof any portion of the earths surface. The portion surveyedis conceived to be projected upon a horizontal plane, calleda plane of reference, upon which all inequalities of sur-face as well as all conspicuous objects are shown in theirtrue relative positions. The simplest and most generallyused method of representing the topography of a givensurface is by means of contour lines. A map containingan outline of a given surface, together with the contourlines representing its inequalities, is called a contour mapof that Fig. 294. Let A B C/\xv Fig. 294, represent the outline of a hill, andsuppose this hill to be gradually submerged in water, thewater rising in successive heights of 10 feet. The flow, orshore line, at each successive rise is a contour line. Thehorizontal lines correspond to the surfaces of the successiveelevations of the water. The points where these horizontallines cut the edge of the hill are projected on the horizontal G74 SURVEYING. line L M. The irregular lines connecting the correspondingpoints of projection are contours. In Fig. 294 they areassumed to be 10 feet apart in vertical measurement. 1293. Conduct of a Topographical Survey.— The manner of conducting a topographical survey will de-pend upon the extent and outline of the surface and the de-gree of accuracy required. If the area be of comparativelyregular dimensions, such as town or park sites, the usualpractice is to lay out the area in squares. The lines of di-vision are the ba
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectrailroadengineering
