2 This is a pre-publication version and it may differ somewhat in content and appearance from the version published in GeoJournal (2002, Vol. 53 (4): 391-406). Please see the final version at: http://dx.doi.org/10.1023/A:1020137029547 Balancing Consensus And Conflict With A GIS-Based Multi-Participant, Multi-Criteria Decision Support Tool Robert D. Feick and G. Brent Hall Department of Geography, School of Planning Faculty of Environmental Studies University of Waterloo Waterloo, Ontario N2L 3G1 Canada 1. Introduction Many land use decision problems are sufficiently complex, controversial and non-routine in nature that their resolution requires not only knowledge, expertise and data drawn from several distinct domains, but also debate of multiple and often conflicting viewpoints, objectives and solution strategies. Despite the promise of Geographic Information Systems (GIS) technology for examining a wide variety of land use issues, it has been criticised for its lack of decision support capabilities in this and other application areas (Hendricks and Vriens, 2000; Towers, 1997; Heywood et al, 1994). In particular, the capacity of commercial GIS to facilitate debate and achieve some measure of balance among different viewpoints has been identified as a major weakness. This capability is constrained by several factors in commercial software, foremost of which is an intrinsic single-user perspective that disregards the multi-interest character of the decision making process and the socially constructed nature of data and analytical methods (Pickles, 1999; Flowerdew, 1998; Jones et al 1997; Goodchild, 1995). A common, and often contentious, planning and land management problem that involves multiple interests is the task of designating sites for specific uses and activities. This problem is intrinsically difficult as it first requires identification of a set of feasible non-dominated sites for the intended use(s) and then an evaluation of non-trivial tradeoffs between the relative merits of each site. Completing these tasks in a pluralistic context is considerably more difficult than by a single decision maker as multiple participants are likely to have different values, objectives, and conceptualisation of issues which are equally likely to be non-coincident or in conflict (von Winterfeldt and Edwards, 1986). The task of seeking a reasonable balance among conflicting viewpoints is complicated further by spatial factors such as externality effects, differentials in land capability, competition among different land uses for specific locations, and the fixed, short-term pattern of land ownership. Hence, partly in response to the criticisms of GIS noted above and partly in response to need, efforts to extend GIS technology to explore and represent the subjective elements of multi-party conflict and decision making have focused on integrating it with multiple criteria analysis (MCA) techniques (Bojórquez-Tapia et al, 2001; Jankowski