Formalizations of geographic common sense are the basis for the design of intelligent GISs that will act and respond as a person would, therefore, empowering people to utilize GISs as reliable sources, without stunning surprises when using a system. The concepts and methods people use to infer information about geographic space become increasingly important for the interaction between users and computerized GISs. While many spatial inferences may appear trivial to us, they are extremely difficult to formalize so that they could be implemented on computer systems. Current methods to derive information about geographic space are limited; therefore, we see a substantial gap between what a human user wants to do with a GIS, and the spatial concepts offered by the GIS. In order to make GISs more useful for a wider range of people, and in order to allow for prediction or forecasting, it will be necessary to incorporate people's concepts about geographic space into the systems, and have them mimic human thinking. If GISs can achieve geographic reasoning in a manner similar to a human expert, these systems will be much more valuable tools for a large range of users, such as family members who are planning their upcoming vacation trip, scientists who want to analyze their data collections, or business people who want to investigate how they performed in various geographic markets.