Show the data
Induce the viewer to think about the substance rather than about methodology, graphic design, the technology of graphic production, or something else
Avoid distorting what the data have to say
Present many numbers in a small space
Make large data sets coherent
Encourage the eye to compare different pieces of data
Reveal the data at several levels of detail, from a broad overview to the fine structure
Serve a reasonably clear purpose: description, exploration, tabulation, or decoration
Be closely integrated with the statistical and verbal descriptions of a data set.