John,
Teaching in school requires 2 basic things.. a professional who has the knowledge in the material being taught and a professional who can properly explain the material in a way that everyone can understand. An effective text book will have a textual description followed by some sort of graphic. (Picture, diagram, chart, graph, etc)Visually this is how people learn. Its a very effective way of observing and understanding the information.
After looking at the pictures posted in this forum, I have learned a wealth of information that quite frankly, I wouldn't have been able to without the use of an excellent visual. Imagination is something that can be poorly misinterpreted.