Graphical excellence is the well-designed presentation of interesting data–a matter of substance, of statistics, and of design.
Graphical excellence consists of complex ideas communicated with clarity, precision, and efficiency.
Graphical excellence is that which gives to the viewer the greatest number of ideas in the shortest time with the least ink in the smallest space.
Graphical excellence is nearly always multivariate.
And graphical excellence requires telling the truth about the data.
The representation of numbers, as physically measured on the surface of the graphic itself, should be directly proportional to the numerical quantities represented.
Clear, detailed, and thorough labeling should be used to defeat graphical distortion and ambiguity. Write out explanations of the data on the graphic itself. Label important events in the data.
Show data variation, not design variation.
In time-series displays of money, deflated and standardized units of monetary measurement are nearly always better than nominal units.
The number of information-carrying (variable) dimensions depicted should not exceed the number of dimensions in the data.
Graphics must not quote data out of context.
Above all else show the data.
Maximize the data-ink ratio.
Erase non-data-ink.
Erase redundant data-ink.
Revise and edit.
(These are paraphrased because Tufte doesn't explain very much in this conclusion; he's even more terse than the above)
Avoid moire vibration which distracts the eye.
Use light grids; heavy grids distract the eye, make certain points harder to distinguish, violate the "data-ink ratio" principle of the above.
Don't make a duck. Unnecessary detail or flourish is counterproductive.
Transformed graphics are better because they display more information per unit space and per unit of ink.
Graphics are almost always going to improve as they go through editing, revision, and testing against different design options. The principles of maximizing data-ink and erasing generate graphical alternatives and also suggest a direction in which revisions should move.
It is a frequent mistake to underestimate the audience's intelligence. Graphics should be as intelligent and sophisticated as the accompanying text.
Well-designed small multiples are
Small multiples reflect much of the theory of data graphics:
For non-data-ink, less is more.
For data-ink, less is a bore.