The purpose of this paper is to examine whether people in general understand elementary spatial concepts, and to examine whether or not naive spatial knowledge includes the ability to understand important spatial primitives that are built into geographic theory, spatial databases and geographic information systems (GIS). The extent of such understanding is a partial measure of spatial ability. Accurate indicators or measures of spatial ability can be used to explain different types of spatial behavior. In this paper I first examine the relation between spatial ability and spatial behavior, then present experimental evidence of the ability of people to understand spatial concepts such as nearest neighbors (proximity), and spatial distributions. A final commentary is made about the possible difference between common sense and expert spatial knowledge, and the implications of such results for the comprehension of space at all scales.