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Definition:
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A method for the measurement of elevation change by comparison of contours on maps of two dates. The area between the later and the earlier instance of each contour is measured. The average elevation change of the region between any two contours is the sum of the area changes (later minus earlier) of the two contours, divided by the sum of the earlier and later areas of the region and multiplied by the difference of the contour elevations. The method, described by Finsterwalder (1953), is now less used, having been superseded by the preparation and subtraction of digital elevation models.
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