This book, describing the result of extended research on how charts/graphs convey information, develops a scheme for describing/analyzing information contained in graphs/charts. A psychological theory of knowledge of the reader and the mental events which occur in attempting to read a graphic display are the two focal points of the book. A comprehensive research program aimed at various levels of difficulty of charts/graphs intended for a wide range of uses and a review of most of the existing literature on charts and graphs (85 references listed) are provided. The literature review is used to develop the analytic scheme/theory and to justify the methods chosen by the research team. A psychological approach is taken because of recent advances in cognitive science which allow a modeling of visual interpretation as something more than a simple recording system. The authors indicated that this is the first attempt at a comprehensive application of applied cognitive science, proving the usefulness of the knowledge being built up, supporting cognitive science in the sense of building a technology on it, and allowing deeper insights into human products and how to make them better. One hundred and thirty figures and tables are attached. (JM)