A method has been developed for obtaining an estimate of relief of an area from the World Aeronautical Charts (scale 1:1,000,000). This consists of determining a value for the lowest elevation and a value for the highest elevation of an area:relief of the area is the difference between these two values. The technique for determining lowest elevations is based on an assumed geometric progression of elevations along a stream;the technique for determining highest elevations depends on an arithmetic progression of elevations on a land surface.
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