How Similarity Shapes Diagrams

Most diagrams communicate effectively despite the fact that diagrams as a group have a minium of conventions and a high tolerance for novelty. This paper proposes that the diversity and felicity of diagrammatic representation is based on three kinds of similarity between semantic propositions and spatial representations that allow people to interpret diagrams consistently with a minimum of effort and training. Iconicity is similarity of physical appearance, polarity is similarity in the positive and negative structure of dimensions, and relational similarity aligns structures so that elements correspond to elements, relations correspond to relations, and so on. In diagrammatic reasoning detected similarities are used to create correspondences between the visual characteristics of a diagram and its semantic meaning, and those correspondences are in turn used to make inferences about unknown or underspecified meanings. 1 Diagrams Represent Many Kinds of Relations in Many Kinds of Ways Diagrams represent many kinds of relations – some spatial, some nonspatial, and some a mix between the two. Diagrams have been used to record activities, ownership, and places (see Tversky, 2001 for a review). Diagrams communicate what has happened in the past, what someone has in mind at the moment, which activities are or are not allowed in a particular place, and what may be expected to happen along a particular stretch of the road. Diagrams sometimes include text, sometimes include conventionalized visual symbols, and sometimes contain novel or unconventional representations. Thus as a group, diagrams seem to function like one of those clubs that lets nearly everyone inside. Perhaps the only necessary conditions for diagrams are 1) that they convey meaning, and 2) that they do so visuospatially. Unrestricted membership and lack of conventions may be a fine way to run a social club, but in a communication system it normally leads to misunderstanding and confusion. One very special characteristic of diagrams is that most diagrams communicate effectively despite the modicum of conventions and the high tolerance for novelty among diagrams as a group. One indicator that diagrams do communicate effectively is that diagrams are often the default communication device for multilingual contexts in which people are likely to need to know something or say something, but do not share a common language that would enable them to do so. Airports, highways, and ports are full of diagrams that communicate things like “This is where you buy a ticket,” “This is where you change money,” and “Do not stand on