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cartographic perspectives 47 Number 43, Fall 2002 hemisphere). Shaded relief illuminated from this direction is highly susceptible to relief inversion, an optical illusion in which mountains and valleys appear to be inverted. Although it is possible to adjust embedded shadowing in aerial photographs to counter relief inversion in relatively flat areas (Rudnicki, 2000), the technique is not applicable in high mountains. Cast shadows - Shadows cast by high, steep terrain often obscure im- portant information on adjacent slopes and flat areas. They also cause drainages to appear misregistered with terrain and can disfigure an image with unsightly dark blotches. Cast shadows are impossible to remove when their density approaches 100 percent. Information overload - Aerial photographs show raw, unfiltered data in all its confusing glory. Untrained readers may find the minute detail to be fascinating, but few actually understand what they are seeing. Inappropriate information - Do we really need to see parking lots, power lines, construction sites, and Christo art? Invisible information - Small buildings, trails and streams often cannot be seen through dense forest canopies. Clouds, which tend to persist over mountainous regions, and their shadows obscure the ground below. No visual hierarchy - From above, a park visitor center and a nearby sewage treatment facility might appear equally significant. Temporal sensitivity - For better or worse, aerial photographs show us a single moment in time. By the time the map is made, an image taken of a farm field could have been replaced with suburban homes, a glacier could have melted, or a winter-bare deciduous forest may be in leaf. Notwithstanding these shortcomings, aerial photographs have been used to produce realistic maps. Most innovative, perhaps, are the South Pacific island maps, including Aitutaki, Cook Islands, produced by the New Zealand Department of Survey and Land Information during the 1970s. On the Aitutaki map, terrestrial areas are shown in a competent and conventional cartographic manner. However, the depiction of water is unique (Figure 2). Using a colorized aerial photograph to show areas below sea level only, coral reefs, shoals, and surf breaks are shown with detail and clarity that can not be achieved with conventional cartographic methods. Relief inversion and cast shadows are not a problem because coral reefs are essentially flat and covered by a layer of shallow water that diffuses otherwise troublesome southeast illumination. By selectively integrating conventional cartography and aerial pho- tography, the Aitutaki map points to the approach used by the NPS for realistic mapping. The NPS uses a multi-disciplinary approach for bringing cartographic realism to its maps. The artistic inspiration of Shelton and Imhof can be found in our products, as can bits and pieces of aerial photographs and satellite images, DEMs, and vector geodata, all of which are combined selectively and with subtlety in Adobe Photoshop and other graphical software applications (Figure 3). Realistically designed NPS maps are • • • • • • NPS APPROACH "The artistic inspiration of Shelton and Imhof can be found in our products, as can bits and pieces of aerial photographs and satellite images, DEMs, and vector geodata . . ."

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