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cartographic perspectives 39 Number 43, Fall 2002 at the resolution of the input data, while matching classes of gray deter- mined by hillshading. Creating accurate hillshaded maps with continuous shades of gray has twice been a goal of cartographers, first with hand-rendered and then with computer-generated maps. The computer reproduction technique of halftoning adds a new control to shading. Halftones, the elemental build- ing block of computer hardcopy displays, can be used to create a pattern, while maintaining the grayscales determined from hillshading. The author welcomes users to experiment with this method and the result- ing images. Copies of the bitmaps used for Figures 7, 9 and 10 and the ESRI ArcView legend files (.avl extension) used to create Figures 16, 17, and 18 can be downloaded from http://www.mbmg.mtech.edu/gis_hill- shading.htm. This website also includes GIS based methods for automat- ing the methods of hachure mapping and those developed by Tanaka (1932 and 1950) that are discussed in this paper. For other recent applica- tions of hillshading methods, see the NACIS Shaded Relief Homepage maintained by Tom Patterson at http://www.nacis.org/cp/cp28/resourc- es.html. The author would like to thank Dr. Robert Ulichney, Dr. Kenneth Sloan, and Vincent Cotter for early comments and suggestions on this halftoning method, and Dr. Jon Kimerling for his perusal of the initial manuscript. Thanks also to Cartographic Perspectives editor Dr. Scott Freundschuh and ONLINE RESOURCES ACKNOWLEDGEMENTS Figure 17. The same hillshaded map in Figure 15 dithered with the halftone patterns from Figure 9 oriented in the aspect direction.

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