Geographic Information Systems (GIS) are widely used in local and regional planning for managing, integrating and visualizing spatial data sets. However, beyond basic levels of decision support, GIS remain largely external artifacts to the decision-making process. This suggests that despite increased analytic sophistication, most GIS software is more suited to providing limited outputs (maps, tables, etc.) than as a tool to support, at anything other than a superficial level, tactical or strategic decision-making processes. To improve the usefulness of GIS as a decision support tool, two needs are apparent. First, decisionmakers require methods that allow them easily to select alternatives most closely aligned with their priorities across a number of relevant criteria. Second, it is necessary to recognize explicitly that most decision-making processes involve multiple participants. Since problem solving is often characterized by multiple and conflicting objectives, methods that contribute toward consensus building are required. This paper describes a prototype Spatial Decision Support System (SDSS) that satisfies these needs through a tight-coupling of GIS functionality and Multiple Criteria Analysis (MCA) techniques. The potential benefits of adopting this approach and future extensions to the prototype are discussed in light of a land use-planning example.