Pretty picture, only possible by falsifying data
Minard turns the route’s curves into more aesthetically pleasing straight lines and exaggerates the latitude difference between the start of the march and Moscow in order to make the Russian capital appear cold when they are really approximately on the same latitude. Again for aesthetic purposes, he moves towns southward along the retreat, in order to keep the visual separation between advance and retreat, when in fact, retreating troops traveled northward across the route they had followed during the advance.
After the Map Companion was published, Dutch cartographer Menno-Jan Kraak published a book that showed how Minard had also taken liberties with the temperature readings.
Detailed reading of the “visualization”
This site provides close-up information on sections of the illustration.
This article details Napoleon’s 1812 Russian campaign, including the pretext for Napoleon’s invasion, the Russia’ resistance, and Napoleon’s retreat.
Blue markers show Napoleon’s advance
Red markers show his retreat.
View Napleon’s March and Retreat from Moscow in a larger map