This map of London was created by John Snow in 1854. London was experiencing a deadly cholera epidemic, when Snow tracked the cases on this map. The cholera cases are highlighted in black. Using this map, Snow and other scientists were able to trace the cholera outbreak to a single infected water pump.

Illustration by John Snow, image courtesy Finavon, Wikipedia

Download this file

  • On March 15, 1813, John Snow was born in York, England. In 1854, Snow, a doctor, was the first person to use the geographic method to keep track of the streets where people were getting cholera, a deadly disease. Because of his map, which marked exactly where people were sick, people deduced that a contaminated water pump caused the cholera outbreak.

    Snow is considered the father of epidemiology, the study of the “patterns, causes, and effects of health and disease conditions in defined populations.”

  • Term Part of Speech Definition Encyclopedic Entry
    cholera Noun

    infectious, sometimes fatal disease that harms the intestines.

    contaminate Verb

    to poison or make hazardous.

    deduce Verb

    to reach a conclusion based on clues or evidence.

    disease Noun

    harmful condition of a body part or organ.