A treatise on surveying, comprising the theory and the practice (1906)
Gillespie, William Mitchell, 1816-1868, Staley, Cady, 1840- · New York D. Appleton · leaf 357
Fig. 509. … either close upon itself, or, if it enters at the edge of the map, itmust terminate at some other point on the edge of the map. 7. The highest contours along ridges, and the lowest contours invalleys, go in pairs; because the lowest horizontal plane that wouldintersect a valley must intersect it in…
Surveying
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