Stage 1. Identify design principles. We identify domain-specific design principles by analyzing the best hand-designed visualizations within a particular information domain. We connect this analysis with research on perception and cognition of visualizations;

Stage 2. Instantiate design principles. We encode the design principles into algorithms and interfaces for creating visualizations; and

Stage 3. Evaluate design principles. We measure improvements in information processing, communication, and decision making that result from our visualizations. These evaluations also serve to validate the design principles.

We have used this three-stage approach to build automated visualization design systems in two domains: cartographic visualization and technical illustration. In the domain of cartographic visualizations we have developed automated algorithms for creating route maps1, 3, 12 and tourist maps of cities. 8 In the domain of technical illustration we have developed automated techniques for generating assembly instructions of furniture and toys2, 9 and for creating interactive cutaway and exploded-view illustrations of complex mechanical, mathematical, and biological objects. 11, 13, 14, 19 Here, we focus on articulating the techniques we have used to identify and evaluate the design principles for each domain. These techniques generalize to other domains, and applying our three-stage approach will result in a better understanding of the

Figure 3. exploded views of complex mathematical surfaces are designed to reveal local geometric features (such as symmetries, self-intersections, and critical points).

 

strategies people use to make inferences from visualizations.

 

stage 1. identify Design Principles Design principles are prescriptive rules describing how visual techniques affect the perception and cognition of the information in a display. In some cases, they are explicitly outlined in books; for example, books on photography techniques explain the rules for composing pleasing photographs (such as cropping images of people just below the shoulders or near the waist, rather than at the neck or the knees). Researchers have directly applied them to build a variety

of automated photo-manipulation algorithms (see the online appendix for examples).

However, our experience is that design principles are rarely stated so explicitly. Thus, we have developed three strategies for extracting and formulating domain-specific design principles: ( 1) analyze the best hand-designed visualizations in the domain, ( 2) examine prior research on the perception and cognition of visualizations, and, when necessary, ( 3) conduct new user studies that investigate how visual techniques affect perception and cognition.

Hand-designed visualizations. We have found that a useful first step in identifying design principles is to analyze examples of the best visualizations in the domain. This analysis is designed to find similarities and recurring patterns in the kinds of information the visualizations highlight, as well as the techniques used to emphasize the information.

Consider the problem of depicting the internal structure of complex mechanical, mathematical, anatomical, and architectural objects. Illustrators often use cutaways and exploded views to reveal such structure. They carefully choose the size and shape of cuts, as well as the placement of the parts relative to one another, to expose and highlight the internal structure and spatial relationships between parts. We have analyzed a large corpus of cutaways and exploded views to identify the principles and conventions expert illustrators commonly use to generate these images. 11, 13, 14, 19 Our process for

FIGure 4. daVId Macaulay, the new way thInGs work

Figure 4. hand-designed “how things work” illustrations (a) use motion arrows and frame sequences to convey the motion and interactions of the parts within a mechanical assembly. our system analyzes a geometric model (b) of a mechanical assembly to infer the motion and interactions of the parts, then generates the motion arrows and frame sequences (c–d) necessary to depict how the assembly works.