Monday, February 20, 2017

Map-making and myth-making in Broad Street: the London cholera epidemic

In the summer of 1854, there was a large outbreak of cholera in London. One section in particular, the Golden Square, and one pump in particular, the Broad Street Pump, have become a sort of legend in epidemiology (the distribution of diseases.) The recognition of these areas comes from the famous Dr. John Snow, who has often been hailed as the one who discovered the cholera outbreak was caused in large part by contaminated drinking water. Snow began investigating the rise in cholera deaths in London after hypothesizing that the public water pumps may have been the starting point for transmission of cholera. Snow went door-to-door, collecting data on the number of deaths at each household finding that a particular water supply company was responsible for more deaths than another company. He then began to investigate the water supply, finding that the water supply resulting in more deaths came from a polluted section of the Thames River, and that the Broad Street pump was used by most of the households in which deaths had occurred. 

The map above show Snow's first map, with the bars indicating the number of deaths per household. While Snow himself made edits to this map after its original publication, further studies of the cholera outbreak reveal that Snow's original hypothesis may not have been correct. It seems to be that the one who really discovered the cause and transmission of the cholera outbreak was actually Edmund Cooper, who created a map prior to Snow's, showing the households in which death occurred, and the number of deaths per household. Cooper's map was based not on the spread of cholera through the water pumps, but rather through the link between the sewage system and the cholera outbreak. 

If we think in terms of GIS, merely finding and mapping information gives the appearance of data, but it does not actually tell us the cause of an outbreak. If this is true, we can then conclude that Snow's maps were misleading in educating the public on the cholera outbreak, and that it was Cooper who discovered the true cause of the London cholera outbreak. 

Brody, H., Rip, M. R., Vinten-Johansen, P., Paneth, N., & Rachman, S. (2000). Map-making and myth-making in Broad Street: the London cholera epidemic, 1854. The Lancet, 356(9223), 64-68. doi:10.1016/s0140-6736(00)02442-9


  1. It is interesting that both Snow and Cooper's findings had different reasons for the outbreak while the two seem like they could possibly be connected. I'm curious to know what was polluting the Thames river, was it possibly the sewage system?

  2. This shows how the credibility the public gives to maps for representing data can often be misleading. Although in this case I agree with Avery's comment that it may be possible that Snow and Cooper claimed two different causes for the cholera outbreak that may actually be from the same source if the water supply from the section of the Thames was used for sewage dumping.

  3. I agree with the above comments. Sometimes public information is manipulated to make people believe certain things. In this case, I don't think that either map is exactly zero-sum, possibly creating a correlation that only appears to be two different things.