Incorporating Expert Knowledge New in fuzzy logic tools ArcGIS 10 By Gary L. Raines, Don L. Sawatzky, and Graeme F. Bonham-Carter For many spatial modeling problems, experts can describe the decision-making process used to predict real-world phenomena: the favorability for locating mineral deposits or archaeological sites, the occurrence of hazards such as landslides or disease outbreaks, the habitat of specific animals or plants, or the optimal site for a business. For most interesting spatial problems, expert knowledge is often expressed in terms such as nearness to some feature or by statements involving sometimes or maybe. Such semantic descriptions are useful but imprecise. Fuzzy logic is used extensively in poorly definable engineering applications such as the anti-lock braking system (ABS) that controls brakes in cars; the focusing and exposure controls on digital cameras; and the control of water intake, temperature, and other settings in high-end washing machines. Fuzzy logic provides an approach that allows expert semantic descriptions to be converted into a numerical spatial model to predict the location of something of interest. In addition to Boolean logic and Weighted Overlay tools in ArcGIS 10, two new Overlay tools—Fuzzy Membership and Fuzzy Overlay—are available. Overlays using fuzzy logic provide more flexible weighting of evidence and combinations of evidence than traditional Boolean or Weighted Overlays. These new tools in ArcGIS are derived from the Spatial Data Modeller (SDM) toolbox developed by the U.S. Geological Survey and the Geological Survey of Canada. [SDM is a collection of geoprocessing tools for spatial data modeling that is available from ArcScripts at http://arcscripts.esri.com/details. asp?dbid=15341.] The Fuzzy Logic tool is just one of many methods available from the SDM toolbox that includes weights of evidence, logistic regression, expert systems, and model validation. A Nonspatial Example Table 1 illustrates a simple example of a nonspatial Boolean and fuzzy logic model through a chart on tallness. Boolean logic deals with 8 ArcUser Spring 2010 www.esri.com