The incremental beautification of hand-drawn diagrams is a process that is poorly understood. Thus implementation of beautification techniques in computer-based sketch tools is ad hoc, with most only supporting the ends of the spectrum: handdrawn and fully formalized. Hand-drawn diagrams are more effective for early design and review but users are more satisfied with formal designs. This suggests that there may be applications for intermediate levels of formality. By understanding the attributes of visual formality it is possible to beautify a diagram progressively, thereby achieving visually consistent intermediate levels of formality. Here we present a taxonomy of the attributes of visual formality and the implementation of this taxonomy into a sketch tool.

The visual fidelity (fidelity) of a design diagram affects perception and design performance. Hand-drawn diagrams are more effective working documents for early design tasks such as user interface designs than the equivalent computer-prepared formal representation. However people prefer more formal representations because they feel that hand-drawn diagrams look unprofessional. Sketch-based design tools make it possible to present partially tidied designs. We have postulated intermediary levels of visual fidelity in a systematic manner and implemented these levels into a sketch tool to evaluate the effect of computerization and fidelity on perception and design performance. Our findings show that: performance decreased systematically with increased fidelity; that computer presented designs decreases performance and that performance was decreased by computerization of the hand-drawn diagrams. In contrast, user satisfaction was higher with increasing levels of fidelity. These results pose challenges to the sketch tools community and further questions for effective computer support for early design.