John Snow, Cartographic Breakthroughs, and the Cholera Epidemic of 1854.

Recently I began to reread one of my favorite historic science books, Stephen Johnson's The Ghost Map, which deals with the great cholera epidemic of 1854 in London.  At the time of the contagion, cholera was believed to be caused by miasma*.  Fieldwork by a pioneering doctor named John Snow established a crucial connection of the cholera victims-- they had all frequented the Broad Street pump for their daily drinking water.  The well of the pump itself was infected with cholera bacteria.  Snow's door-to-door surveying work established the cause of the contagion, as well as the notable fact that cholera is water- rather than air-borne.

No, no, cartoons are supposed to be funny.

Snow's work is to great interest to cartographers as his resulting map provided particularly damning evidence that the pump was the source of the disease.  He conducted street level research and found that although certain other pumps were closer to victims as the crow flew, the Broad Street pump was usually the closest to the victims based on street traffic paths.  His published map is below:

Snow map 1854, click to enlarge

Snow also stumbled upon voronoi style mapping, and below is his famous map with the voronoi region overlay:

Voronoi map, click to enlarge

*definition of miasma (noun):  a mysterious mist that killed thousands before it vanished entirely in the face of modern science, never to be seen again.