Cars

cartographic perspectives 53 Number 43, Fall 2002 cover selections as opposed to generalized selections (Figure 9). Alternat- ing textured/nontextured areas produces a tessellation that compliments the texture pattern as a whole. With some classes of land cover, such as forests, a slight amount of 3D embossment (known as bump mapping in 3D applications) applied to forest polygons themselves suggests a for- est edge rising above adjacent non-forested areas (Nighbert, 2000). The orientation of the tiny highlights and shadows on an embossed 3D tex- ture must synchronize with the illumination and shadows on the shaded relief—usually from an assumed light source in the upper left. In general, textures should be used sparingly on a map. Keep in mind that not every type of land cover warrants or is suitable for texturized portrayal. On NPS maps land cover textures are mostly used to depict forests, glaciers, lava flows, and rocky peaks. Other classes of land cover are left untextured to give the reader's eyes a place to rest. When aerial photograph textures are not suitable for texture substitu- tion, manual touchups and synthetic texturing (both done in Photoshop) are the options of last resort. If these techniques must be used they should be printed lightly and applied to polymorphous features, such as sand dunes or glaciers, where cartographic accuracy is elusive under the best of circumstances (Figure 10). Illuminated relief The illuminated relief technique enhances shaded relief combined with land cover textures. Normally, combining shaded relief and land cover textures on a map involves graphical compromise. Together these ele- ments are not as effective as when they stand alone, especially shaded relief, which has a wispier appearance compared to land cover textures. When illuminated relief is used, supplemental illumination and shad- owing enhance topographic modeling by also lightening and darkening land cover textures. The technique uses adjustment layers and alpha channels to manipulate the hue, saturation, and brightness of selected areas on a shaded relief map. By using multiple adjustment layers that build upon one another, complimentary illumination and shadow colors can be made gradually more intense at higher elevations to suggest al- penglow (Figure 11). Conversely, substituting gray-blue for dark gray in "The orientation of the tiny highlights and shadows on an embossed 3D texture must synchronize with the illumination and shadows on the shaded relief . . ." "Normally, combining shaded relief and land cover textures on a map involves graphical compromise." Figure 9. Texture substitution: Kenai Fjords National Park, Alaska. (top) Detailed land cover gener- ated in ERDAS from SPOT and Landsat satellite images. (bottom) The same land cover reduced from 18 to 5 categories on the park visitor map. The substituted forest texture was cloned from an aerial photograph taken near San Francisco, California.

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