…to understand human cognitive functioning, we must understand how people code the locations of things and navigate around the world, and how they represent and mentally manipulate spatial information (p 2). A fundamental distinction is that the location of objects can be coded in two basically different but coordinated ways: with respect to external landmarks, or with respect to the self (p 14). A core idea in developing competence…is understanding how to meaningfully enumerate rectangular 3D arrays of squares and cubes, respectively (p 897).