- GeoRef, Copyright 2004, American Geological Institute. Reference includes data from Bibliography and Index of Geology Exclusive of North America, Geological Society of America, Boulder, CO, United States
"Simple arithmetical techniques are set out whereby planimetric data, of the kind used in constructing area-height diagrams, can be made to yield additional quantitative information useful in description and comparison of relief. The most useful is an expression for mean available relief, which takes account of the form as well as of the height of interfluves. It is also shown how the depth of dissection of a datum surface can be mapped and measured."