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An easy variation is to substitute for the dotted line a rubber band upon which the equal divisions of the difference in altitude have been marked. By stretching the rubber band between the station and the peak, one can easily determine whether the elevation of any intervening obstruction is higher or lower than the elevation division marked on the rubber band at that point. If a distance of more than a few miles exists between the station and the peak, allowance must be made for curvature of the earth and refraction of light by the atmosphere. Contour topography.—The most accurate method of representing land forms upon a map is provided by contour topography, the method used throughout the United States in maps of the Geological Survey. On the |
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