A post from data.visualisation.free.fr

Above all, show the data

In his seminal book, Edward Tufte proposed some rules for good visualisation practices. He encourage truthfulness, some sort of data transparency allowing the reader to "see the data" and  even defined a "lie factor" as the ratio between the printed representation of the data and the real underlying values in the dataset. Nobody doubt that one should design a data visualisation with honesty, and avoid any temptation of cheating or  little arrangements with the data.  But some did, and there were right to do so!

Early ``cheaters''

Charles Minard’ (1869) Napoleon’s Russian campaign map graph was quoted by E. Tufte (again) as “the best statistical graphic ever drawn”. This is probably true, and Minard was a pioneer in thematic cartography and wanted to let the data “speak to the eyes.” Hence, we can spot some approximations in the design of the map, its lack of projection reference (as quoted by Michael Friendly), but also some arrangements in the aggregation of flows leaving and then rejoining the “great army”. This looks really nice and is really a great map. 

Some approximations for a storytelling map (a brilliant one)

In reality Napoleon’s army was divided into several branches which followed different paths, but which are not showed on Minard’s maps for clarity (see Martin Grandjean for details). So, Charles Minard simplified the data representation on purpose.