John Snow is viewed by many as a pioneer in disease mapping. For the 1854 cholera outbreak in London's Broad Street region, he presented two maps. The first was shown on December 4, 1854 at a meeting of the London Epidemiological Society. Several months later he published this map in his book, On the Mode of Communication of Cholera, 2nd Edition. He used bars to represent deaths that occurred at the specified households. There were several minor errors in this map which were later corrected. One such error was in the place of the Broad Street pump. In his original map, the pump was located at the exact corner of Broad Street and Cambridge Street (see below).
The following Spring, John Snow submitted a second map of the same area to the Cholera Inquiry Committee of St. James Parish, which was issued as part of the Committee's general report in July 1855. By then, Snow had noticed that the pump was not in the right location (see below).
Many years later, other map makers attempted to improve on John Snow's map by using dots rather than bars to represent each death. One such map that appeared in cartography books was drawn about 1960 by Regmarad, a one-named illustrator.
Yet Regmarad's map was filled with errors and is not generally cited in the epidemiologic literature. For example, in the block where the Broad Street pump was located, there were 66 deaths; 18 of these deaths occurred at one location and 5 at another (both seen in red). .
For the same block, Regmarad moved the pump to the middle of Lexington Street (rather than in from the corner of Cambridge Street) and showed two fewer deaths in one location (16 versus 18) and one less in another (4 deaths versus 5), for a total of 63 rather than 66 as appeared in both Snow maps.
John Snow, while not a cartographer, did very well in presenting a visual overview with his original maps.
Snow, J. On the Mode of Communication of Cholera, 2nd Edition, 1855.
Stamp, LD. Some Aspects of Medical Geography, Oxford Univ. Press, 1964.
Vinten-Johansen P et al. Cholera, Chloroform, and the Science of Medicine: A Life of John Snow, 2003.