The Ghost Map

I read The Ghost Map: The Story of London's Most Terrifying Epidemic--and How It Changed Science, Cities, and the Modern World this week. It started out as a gripping recounting of the 1854 outbreak of cholera in London and in its wake, the two men who unraveled the mystery of how cholera spread. Steven Johnson includes fascinating contextual details about the London of the times, including graphic descriptions of the sanitation situation and the early problems of dealing with a large urban center that I had to skip over. YUCK!

I was most intrigued by the story of John Snow, a practicing physician who also pioneered early methods of epidemiology by combining geographical data and the physical spread of cholera compared to the location of water sources----the precursor to our modern day GIS. His battle against the proponents of cholera spread by miasma--the airbourne spread, mostly indicated by foul smelling air--was based in the scientific method. Prior to the 1854 outbreak, he systematically attempted to show how the water supply was responsible by conducting an experiment. He was able to find several individual neighborhoods--thus controlling for poverty, foul smells, and other supposed causes--that had two different suppliers of water. Because residents had no clear idea who provided their water, Snow went door to door collecting samples of water since one company's water had four times the salinity of its competitor. Johnson characterizes him as utilizing skills not as a physician, but as a sociologist and demographer. The logic of his approach to the problem of cholera spread was so clear and perfect. I loved it. To design a study like that!

During the outbreak, he collected data on the deaths, location, and their proximity to the Broad Street pump, the source of the cholera bacteria. He persuaded the local council to remove the handle to the Broad Street pump to prevent the spread of cholera, and then spent time after the outbreak documenting all his analysis.

This map is the lynchpin of Snow's analysis which shows the proximity of the outbreak deaths to the Broad Street pump. Later, he expanded his map to show distances not just as the crow files, but the walking distances to water.

Where the book becomes disappointing is when Johnson deviates from the historical story of the outbreak and starts to draw too many, too far- reaching applications to the modern day. I thought the application to contemporary water problems was fine--cholera has not been eradicated in the world at large and urban centers in developing nations face the same problems that London did in the mid-1800's. But, he went too far. Talk about whether or not the world would turn into a city-planet--what scenarios would cause people to migrate to either the cities or rural areas. I lost interest at the end.