• dimensionality-displaying multivariate data on the two-dimensional surface of paper or computer screen
• resolution-displaying large amounts of data in a limited space, at task more difficult on computer screens than on paper

Tufte's most frequently-cited historical example is the classic produced by Minard in 1861. This combination data map and time-series describes the fate of Napoleon's army during the invasion of Russia in 1812-1813. According to Tufte, this chart illustrates five key principles of good information design:

• force visual comparisons (the upper lighter band showing the large army going to Moscow vs. the narrow dark band showing the small army returning)
• show causality (the temperature chart at the bottom)
• capture multivariate complexity (size of army, location, direction, temperature, and time)
• integrate text and graphic into a coherent whole
• illustrate high quality content (complete and accurate data, presented to support Minard's argument against war)

• place comparisons adjacent to each other, not sequentially (people forget if they have to go from page to page )
• use the smallest effective differences (i.e., avoid bold colors, heavy lines, distracting labels and scales)

Tufte emphasized that displays of information support thinking and analytic tasks. Therefore, his principles of design are derived from cognitive principles. He reserved his greatest scorn for the perpetrators of "chart junk," the gratuitous use of icons, false 3-D effects, outlandish colors, and other effects made easy by the computer. Chart junk often reflects weak data or poor thinking. "Excel itself is not the problem."

This last remark was typical of Tufte's method of using humor to help deliver his message. When discussing Galileo, he described him as having a modern voice: direct, blunt, somewhat sardonic. This description would fit Tufte himself, who at one point observed that only two businesses refer to their customers as users.

Tufte addressed many current issues. He derided the misuse of the "evil doctrine" that recommends just seven items on a page, saying that this rule was established for memorization and should not be applied for other situations. Introductory web pages, he said, should present as much information as possible, since web surfers are coming to scan the contents, not memorize them.

Not all examples were of good design. Tufte analyzed the space shuttle Challenger explosion, arguing that poor information design led to the fatal decision to launch. Thiokol engineers had recommended not to launch, based on O-ring damage in previous low temperature launches. But they never made the simple chart of damage vs. temperature that clearly showed the causal relationship. NASA, reluctant to delay the launch, never saw the data that might have prevented the disaster.

Tufte's books--The Visual Display of Information, Envisioning Information, and Visual Explanations--contain wondrous examples of information display together with his cogent analyses and recommendations. Copies are available from Graphics Press at (800) 822-2454.