In making data presentations, it is all too easy to make them overly complicated while not communicating any data of real value. Much like How to Lie With Maps, this books serves to try to reduce presentation error. Tufte admonishes designers to steer away from cute but inaccurate graphics, removing “chart junk” (styles or designs that distract from the data by making it more difficult to read) and killing “ducks” (which he describes as “when the data measures and structures become Design Elements, when the overall design purveys Graphical Style rather than quantitative information”). The book has a series of solid graphic design principles that can help reduce “ducks” and present data in clear, more readable layouts.
Interesting tidbit: Tufte is a strong advocate of altering line shape (mostly widths) on maps to communicate additional information rather than create new data sets. A prime example is Minard’s map of Napoleon’s march where the line angle is the path of travel, width is the size of his army and color is the direction of travel (brown is advancing and black is retreating).