ABSTRACT
Pictures are made for many different purposes (Hagen, 1986; Hochberg, 1979). This discussion is about pictorial displays whose primary purpose is to convey accurate information about the three-dimensional spatial layout of an environment. We should like to understand how, and how well, pictures can convey such information. I am going to approach this broad question through another question that seems much narrower. We shall find, however, that if we could answer the narrow question, we should have made a good start on answering the broader question as well.
