April 16, 2007, 2:15 pm
On Tufte and Napoleon’s March
By Mac McBurney
In February, the Dynamic Diagrams staff made a field trip (some might say pilgrimage) to Edward Tufte’s day-long seminar, “Presenting Data and Information.” If you’ve ever heard of Edward Tufte, you have probably seen Napoleon’s March to Moscow, Charles Josef Minard’s visual explanation of Napoleon’s disastrous attempt to conquer Russia in 1812.
Tufte says, “it may well be the best statistical graphic ever drawn.” The graphic appears repeatedly in Tufte’s books, posters and brochures. At the recent seminar, I realized that the image has become a defacto corporate logo of Tufte and Graphics Press. At the seminar, the graphic was used in a sign directing participants from the hotel lobby to the upstairs lecture hall. It worked: Napoleon’s March quickly caught my eye and confirmed I was headed in the right direction.
Conventional wisdom v. six-variable masterpiece of information design
Because Napoleon’s March is so innovative, so lauded, so pervasive in Edwardtufteland and so emblematic of Tufte’s teachings, it was (I’m chagrined to admit) not easy for me to see that it undermines, rather than supports, the conventional view of the historical events. (Thanks to Piotr, creative director at d/D, for leading the way.)
Minard created his map to show the horrors of war. Tufte uses it to explain grand principles of data display. Both are succeessful, but Tufte misses an opportunity to emphasize just how powerful Minard’s graphic is. Tufte repeats the popular belief that “General Winter” defeated Napoleon’s army. I haven’t studied the history since high school, but this fits the image that sticks in my head: soldiers freezing to death.
In fact, according to Minard’s map, nearly three times as many French soldiers were lost (never mind the Russians) before the retreat and before the coldest weather. 90,000 died on the retreat–horrible to be sure — but 250,000 were lost before that. Only because the map follows Tufte’s grand principle number one, show the data, are we able to really question the conventional wisdom, ask useful questions and formulate alternate narratives. Now that I’m re-thinking my own understanding, I wonder why Tufte even mentions General Winter as the moral of the story.
In addition to temperature itself and the impending threat of winter, I suspect another factor strengthens the prevailing interpretation: recency bias. Only ten thousand French soldiers lived to tell the tale. They had just endured three months of immense suffering and witnessed the deaths of 90,000 comrades (90% of the retreating force). It’s hard to imagine their state of mind, but the previous summer was probably a distant memory.
There are seven variables, not six. See the last chapter of my book, The Grammar of Graphics (Springer, 2005).
Posted by Leland Wilkinson on November 17, 2007 at 8:41 pm