The Topography of Disease

While Snow’s analysis was focused on one possible explanation for the outbreak, and his argument rested on the visual clarity of his map, Acland took a more statistical approach that considered many potential disease factors. In addition to mapping victims, Acland included sites that had previously been deemed unhealthy (brown dots), those that had subsequently been cleaned up (brown circles), streams that were unpolluted, and those that had been contaminated (dashed lines), including point sources of the contamination such as outflows of raw sewage (see close-up below). Acland’s map neatly backed up the miasmatic theory, suggesting that the toxic air would collect and remain in low areas with less wind.

Source: blogs.scientificamerican.com