"Peirce (1932: 2.278) distinguishes two kinds of icons: pictures and diagrams, the latter of which he illustrates with the example of an electrical wiring diagram in relation to the wiring itself. But the difference between a picture and a diagram, as Peirce himself notes, is relative. The picture always abstracts from some features of the object it portrays, e.g., three-dimensionality in painting. The diagram is simply more abstract. The difference, then, is one of degree and not of kind."