Figure 3.19 Mapping disease. This map was constructed by London physician John Snow. Snow was skeptical of the notion that “bad air” somehow carried disease. He interviewed residents of the Soho neighborhood stricken by cholera to construct this map of cholera cases and used it to trace the outbreak to the contaminated Broad Street pump. Snow is considered to be a founder of modern epidemiology. (Source: Courtesy of the John Snow Archive.)