The Importance of Both Diagrammatic Conventions and Domain-Specific Knowledge for Diagram Literacy in Science: The Hierarchy as an Illustrative Case

As noted so eloquently by Lynch (1990), diagrams are critically important in science. Hegarty, Carpenter, and Just (1991) classified scientific diagrams into three categories: iconic, schematic, and charts and graphs. Iconic diagrams, such as photographs and line drawings, provide a depiction of concrete objects in which the spatial relations in the diagram are isomorphic to those in the referent object. Accurate representation of spatial relations can be critical, for example to distinguish the venomous coral snake from the similarly-colored non-venomous Arizona mountain king snake. In the life sciences, iconic representations help students understand the structure of objects that are not easily open to visual inspection. For example, side-by-side drawings of the stomachs of people and cows, with the parts labeled, would provide insight into why digestion works differently in these two taxa.