Designers use their minds to de ne and solve complex problems containing many elements, more than their limited short-term human memory can easily retain. To augment their memory, they create external representations, objects such as notes, sketches, drawings, or physical models. While these external representations are often thought of as being the design, each captures only aspects of it. In this way the designer is able to grapple with complex con gurations and pay attention to di erent elements of the design without losing track of information while their attention is elsewhere. Representations have additional value when they can be used as the foundation for computational evaluation or analysis of the design proposal, or as communication tools by which to convey design intent to clients, contractors, or other interested parties.