Philosophers and practitioners commonly distinguish between descriptions, depictions and diagrams as visual representations. But how are we to understand the differences between these representational types? Many suggestions have been made, all of them unsatisfactory. A common assumption has been that these representational types must be evaluated in terms of the presence or absence of a single property. I argue that this assumption is both questionable and overly restrictive, and advance a two-property analysis in terms of what I call Assimilability and Discretion. I argue that this analysis allows us give a general differentiation of the various types and to understand better what factors could affect changes in classification. This suggests an outline framework for empirical research. Philosophically, it can also be used to capture a core idea of perspicuousness, and to ground an argument for the general perspicuousness of diagrams as a representational type.