In this paper, the authors evaluate map overlay, a concept central to geospatial thinking, to determine how it is naively and technically understood, as well as to identify when it is leaner innately. The evaluation is supported by results from studies at three grade levels to show the progression of incidentally learned geospatial knowledge as student mature and develop more complex thinking strategies. The findings have been useful for understanding when and how geospatial concepts are learned innately. The results of the studies will be discussed in terms of creation of a hierarchy of concepts and use of "minimal" GIS for geospatial education.