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The Representation of Topographic Information on Maps: The Depiction of Relief

The land surface is often a dominant component of topographic maps, yet relative to horizontal distances, changes in altitude are very small. So why should relief depiction be a key element of topographic map design? One obvious reason is that we are very small in comparison to hills and mountains and therefore cartographers exaggerate our subjective response to these land forms to match our subjective impressions. Furthermore, a minor change in altitude can also be accompanied by a dramatic change in environment, a variation to which we are also very sensitive. Hills and mountains are a very visible part of the landscape and offer map users a fundamental link between the real world and the abstract symbols of the map. Terrain portrayal is often a source of criticism both for its failure to create an impression of relief in the mind of the map user but also for its interference with the legibility of other map information. The successful representation of relief on a topographic map therefore depends on how well the map conveys a subjective impression of the landscape and not merely how it records its planimetric and altitudinal variation. With the increased quality and quantity of elevation data, developments in computing and reprographic techniques and the ever growing popularity of maps, the portrayal of the land surface form has taken on special signicance in recent years. However, only relatively recently has literature become available that attempts to aid the cartographer solve the fundamental problem of recreating the three-dimensional surface of the earth by two-dimensional symbols. What follows is not an exhaustive treatise on relief portrayal, but rather an exploration, with examples, of how cartographers continue to grapple with this age-old problem. Any study of relief representation must refer to Imhof’s classic work ‘Cartographic Relief Representation’ (Imhof, 1982). Not restricted to pure descriptions of the various methods, this work provides an introduction to methods of topographical survey with special reference to accuracy in measuring terrain surfaces and the interpretation of relief from air photographs. Other concepts such as the theory of colours and the interplay of map elements form the foundation of the detailed treatment of the different methods of relief representation. By comparison, other works may seem rather supercial. Nevertheless, the standard cartography texts, notably Keates (1989) and Robinson et al. (1995), provide adequate introductions. Relief portrayal has provided a subject for experimentally based studies in map legibility and perception. Studies by Patton and Crawford (1977), Potash, Farrell and Jeffrey (1978), and Phillips, De Lucia and Skelton (1975) have sought to develop scientic design principles based upon the objective testing of cartographic products utilizing experimental techniques already established by the human factors engineers, psychologists and physiologists. Their success is open to question. Nevertheless, reference to these works should at least alert the map designer to the possible effects that different relief portrayal methods may have on map information accessibility and interpretation, and more signicantly to the diversity of the needs and abilities of the map user. Topographic maps produced by national mapping agencies offer a range of relief representation methods. As with all elements of map design, the method of relief portrayal adopted will depend on the perceived purpose of the series and the needs of the majority of its users. National mapping organizations have to choose between conicting interests The Cartographic Journal Vol. 40 No. 1 pp. 17–26 June 2003 17 # The British Cartographic Society 2003