Book Review: The Ghost Map

April 20, 2022

This is the story of Victorian London and the cholera outbreak that occurred there in the summer of 1854. It began in the neighborhood of Soho, centered on Broad Street. Over 120 people died in a three day period in Soho, and a local doctor named John Snow, along with young clergyman Henry Whitehead both set out to investigate, trying to understand how the outbreak had happened.

Author Steven Johnson works to provide a comprehensive view of the city, the times, the events of the outbreak, and the confluences and synchronicities that led to the breakthrough in understanding of the spread of cholera. 

He starts with a description of the London underclass. These were the bone-pickers, the mud-larks and the “night soil” men, among others, whose scavenging jobs helped to provide the basic sanitary services that were not yet a centrally delivered feature of city living. Victorian London was the first city whose population reached 2 million souls, and without those central services it was a smelly, filthy place. As the city had not yet figured out how to successfully deal with its human waste needs in particular, outbreaks of diseases like cholera were the result. 

But at the time no one understood what caused cholera. In smelly London, the prevailing wisdom was that all communicable diseases, cholera included, came from bad smells – known as miasmas. It wasn’t until the work by Snow and Whitehead that it began to be realized that cholera in fact is waterborne, resulting from infected human waste contaminating drinking supplies.

Snow and Whitehead independently visited the homes of the sick, trying to understand the course of the disease even as it was happening. Snow, one of the first anesthesiologists in England, already had spent time researching cholera and had come to believe that it was spread via water and not through the air.  In his investigations in Soho, Snow was able to determine that a single water pump on Broad Street seemed to be the source of the infection. He convinced the local authorities to remove the pump handle, after which the number of cases fell.

Whitehead did not believe Snow’s analysis. It was only after seeing Snow’s mapping of the deaths in the neighborhood – his “ghost map” – that he became convinced. Together they were then able to unravel the sequence of events and locate the outbreak’s index case – it’s patient zero. Their groundbreaking work set the bar for all future epidemiological studies, and did so well before the germ theory of disease was even established. The map that Snow drew has been reproduced in “countless textbooks on cartography, information design, and public health.”

The book is a well done combination of a lovingly evoked word painting of Victorian London, and a medical thriller. There are a couple of miscues however. For one thing, even though the book is named after Snow’s famous map, the map itself does not appear anywhere in it (though a portion of the map is used as a faded set piece before each chapter). The other miscue is the epilogue, in which Johnson tries to use Snow’s map work as an entry point to discussing several modern problems, and which rambles on for twenty four pages without clearly hitting its mark. Skip the epilogue – you won’t be missing much.

Rating: Four Stars

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Steven Johnson’s 2006 TED Talk 

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