ABSTRACT
Native Londoners or people who lived there a long time and who travel on the underground have memorized or internalized large sections of it, and don't have to bother with it; but for others, it is a diagram of compelling interest. The roundel is a symbol of undergroundness in general and the diagram is a symbol, at a lower level of abstraction, of the underground as an entity or as a system with its eight different lines, interchanges. The diagram is both a symbol and a guide and provides what might be called representational mastery. The key to the underground is the interchange system. Since the underground was not built as one system, but represents a merger of a number of formerly separate ones, it contains numerous redundancies. Despite the redundancies and certain inconveniences, the underground is an effective system.
