Sketches are produced in many domains to communicate with self or others. They are a kind of external representation serving as a cognitive tool to augment memory and information processing by relieving the mind of some of those burdens. Sketches schematize. They do not portray reality; rather they convey conceptions of reality. Sketches use elements and spatial relations on paper to represent elements and spatial or abstract relations in the domain of interest. They incorporate relevant information and omit irrelevant. As such, they reveal people’s conceptions of domains.. An analysis of sketches of routes, for example, reveals that they segment routes around action points, typically turns. Order of drawing reflects mental organization of the domain. From sketches, novices extract structural information about the spatial relations among elements. Experts are also able to extract functional information, information that must be inferred from rather than directly extracted from sketches.