The Ghost Map

I’ve almost finished reading The Ghost Map by Stephen Johnson. It tells the story of the London Cholera outbreak of 1854 and how how Dr. John Snow, an anesthesiologist, used data collection techniques and information design to develop a compelling map of cholera deaths that helped to isolate the source of the disease, stop the spread of that outbreak and ultimately change the understanding of how cholera is spread.

As the title suggests, much of it comes down to a single map. I’ve included two versions of the map here.

A few thoughts:

1. A picture is worth a thousand words. The first map, slightly enhanced to make the key information stand out (red lines for cholera deaths and blue circles for water pumps), clearly shows the proximity of deaths to the Broad Street Pump, which was ultimately found to be the source of the contaminated water containing the cholera bacteria. 
2. TMI. There is such a thing as too much information. Prior versions of the map were tossed because the key information was obscured by other data. Focus on The Essential
3. Get granular. The top map is compelling. When you overlay the line where the Broad Street pump was the closest water access (bottom picture) the conclusion jumps out at you. The key to the second map (a voronoi diagram, new to me) is knowledge of the local foot traffic patterns. The line was drawn not from a simple radius around each pump, but from an understanding of which pump was the closest walk to each residence, gained by speaking with residents, with the help of Rev Henry Whitehead, a local parish priest. 
4. Conventional wisdom is entrenched and often wrong. Dr. Snow’s finding were not widely adopted in his lifetime. The competing and widely held “miasma theory” (that the disease was in the air) held on for another 20 years before it came to a definitive end.
5. Having the courage of your convictions. Much of the data Snow and Whitehead gathered was from being in the midst of the cholera outbreak when the most widely held belief was that the disease was in the air. 

One of my intentions for the new year is to cut down on random reading and focus on my list, but I'm glad I stumbled across The Ghost Map. I highly recommend it, but be warned, much of the early part of the book covers the lack of sanitation in 19^th century London. You’ll learn about “night soil” and dozens of other terms for shit. It’s a well written, educational and entertaining read.