This study identified five subdimensions of spatial habits of mind--pattern recognition, spatial description, visualization, spatial concept use, and spatial tool use--and created an inventory to measure them. In addition, the effects of GIS learning on spatial habits of mind were investigated. Pre- and post-tests were conducted at the beginning and end of a semester-long GIS course. The results suggest that the inventory is a reliable and valid instrument for measuring spatial habits of mind. Analysis of student responses revealed that completion of a GIS course enhanced their spatial habits of mind. It is believed that this research is relevant to a wide range of disciplines whose practitioners are interested in spatial literacy. (Contains 6 tables and 2 figures.)