John Snow (cholera map)

John Snow was a 19th-century physician who is best known for his pioneering work in epidemiology during a cholera outbreak in London in 1854. He created a map plotting cholera cases in relation to water pump locations, revealing a clear pattern: areas supplied by a contaminated pump had higher infection rates. This evidence helped him conclude that cholera was spread through contaminated water, not "bad air" as commonly believed. His map effectively demonstrated the importance of clean water and laid the groundwork for modern public health and sanitation practices.