1. The Effect of Shaded Relief on Map Information Accessibility
2. Joel L. Morrison, 'The relevance of some psychophysical cartographic research to simple map reading tasks'. Paper read at the I.C.A. Technical Conference, Moscow, August 1976.
3. A. H. Robinson and R. D. Sale, Elements of Cartography, 3rd ed., New York: John Wiley, 1969, p. 178.