The Ghost Map by Steven Johnson
The Ghost Map by Steven Johnson documents the London cholera outbreak in 1854 and the work of two citizens to convince the world that cholera was transmitted through the drinking water supply. The two characters are John Snow, a doctor, anesthesiologist, polymath and amateur epidemiologist (a field he largely founded). And Henry Whitehead, a cleric in the local church and debunker.
The reigning theory of disease at the time was 'miasma', disease was smell and in the dense urban environment of Soho at the time, it really smelled. And susceptibility to disease indicated moral failure or some kind. The poor of the Soho neighborhood where the cholera struck were poor because of these same moral failings, at least according to the classist ideas of Victorian London. Snow applied a clever use of statistics, interviews, data collection, and visualizations (dot maps and voronoi diagrams) to determine that the outbreak was originating from a single pump and that water was the culprit. Whitehead provided the social and local knowledge of the population to find the index case. Between them they convinced authorities and the broader scientific world that the disease came from human waste in the water supply. This lead to one of the greatest engineering projects of the 19th century: the London sewage system.
Johnson weaves a great story around these two characters citing lots of primary sources and reproducing the maps and visualizations. These two really changed the world and Johnson spends some time explaining how conquering disease in urban environments lead to a boom in urban density which has largely been a positive for humanity. Once he wraps up the main story, the last section of the book takes some weird turns into predicating the future and half baked treatise on the future of human density. There's also a weird off theme section on the 9/11 attacks and their relation to density. It was really out of place. But the bulk of the book is fascinating. I'm looking forward to chasing down more of Snow's work, I'd love to see more about the statistics he used. I'm starting with this site.