Map-making and myth-making in Broad Street: the London cholera epidemic, 1854

In the 1854, London had a cholera outbreak which Dr. John Snow stated was transmitted through drinking water. What Dr. Snow did then, was mark on a map the location of homes where people had died because of the disease. He noticed that a certain neighborhood was getting water from a private company, but the water was coming from the Thames River, which at the time was very polluted. As soon as the water pump was removed from that river, the epidemic diminished.

During the cholera outbreak, there were two competing water companies that had water pipes in the same streets. He wanted to compare them and find out exactly which one was the cause of the deaths. For his maps he used black bars to indicate the deaths. He went door to door, investigating where exactly the deaths had occurred to trace it back to a pump.

The following map shows us the deaths within a metropolitan neighborhood. The map includes the houses marked by dark black bars and the bars behind them indicate the amount of deaths within each house. He and another investigator, Cooper made several maps along the way depicting the neighborhoods in different ways trying to figure out the outbreak. As the investigations went on, the government began to use this map and fixed it up a bit, making the markings clearer to ultimately find the breakout of the epidemic and outbreak.