Edward R. Tufte has been leading force in the visual assessment of scientific data.  His book, The Visual Display of Quantitative Information (Graphics Press, Cheshire, Connecticut, 1983), contains a half page on John Snow's Map 1. 

An early and most worthy use of a map to chart patterns of disease was the famous dot map of Dr. John Snow, who plotted the location of deaths from cholera in central London for September 1854. 

Tufte's dot map

Deaths were marked by dots and, in addition, the areas eleven water pumps were located by crosses. Examining the scatter over the surface of the map, Snow observed that cholera occurred almost entirely among those who lived near (and drank from) the Broad Street water pump. He had the handle of the contaminated pump removed, ending the neighborhood epidemic which had taken more than 500 lives. The pump is located at the center of the map, just to the right of the D in BROAD STREET. Of course the link between the pump and the disease might have been revealed by computation and analysis without graphics, with some good luck and hard work. But, here at least, graphical analysis testifies about the data far more efficiently than calculation.

Reference

E.W. Gilbert, "Pioneer Maps of Health and Disease in England," Geographical Journal, 124 (1958), 172-183.

See Map-making and Myth-making for a different view of the role of maps in Snow's Broad Street investigation.

Read The Map as Intent: Variations on the Theme of John Snow for a critique of Tufte's use of Snow's map and distortions that have occurred over time.

Return to John Snow site