Once upon a time in a City called London lived a Doctor by the name of John Snow. Greatly vexed (and losing valuable patients) during the city’s latest epidemic of Cholera, the visually minded physician began mapping out cases in one of the most affected neighborhood and, using his map, was able to trace the epidemic to the local wells. Of incredible historical significance, this Victorian map is a masterpiece of cartography, investigation, and visualization, and an Edward Tufte favorite.
Lessons learned? Even the most simple, effective visualization causes people to think about the subject at hand differently. Oh, and don’t dump raw sewage into your city’s drinking supply.