The authentic John Snow, a precursor of Geolocation

Source: Dev.to

Background

John Snow (United Kingdom, 15 Mar 1813 – 16 Jun 1858) was an English physician who is now regarded as a precursor of modern epidemiology and geolocation. While many today associate the name “John Snow” with the fictional character from Game of Thrones, the historical John Snow is famous for his groundbreaking work on the cholera outbreak in London in 1854.

The 1854 Cholera Outbreak

Snow investigated a severe cholera epidemic that struck the Soho district of London, in which roughly 700 people died within a single week. At the time, the prevailing miasma theory held that disease was spread through foul‑smelling air. Snow challenged this view by proposing that contaminated water was the true vector.

Mapping the Outbreak

To test his hypothesis, Snow created one of the earliest examples of a geographic information system (GIS). He overlaid several layers on a map of the neighbourhood:

• Water pumps – marked as points labeled “pump.”
• Deaths – represented by stacked black lines at each residence where a death occurred.

The visualisation revealed a striking concentration of deaths around the Broad Street pump. More than 70 % of the cases were linked to households that obtained water from this pump.

Exceptions and Clarifications

Snow also accounted for outliers:

• Workers in a workshop and a distillery avoided illness because they used private well pumps.
• Some deaths far from Broad Street were explained by victims’ recent visits to the area for work or family reasons.

Intervention and Outcome

Further investigation suggested that the pump’s water had been contaminated by sewage, possibly from a baby’s soiled diaper that had been discarded into a nearby cesspit. Snow persuaded the authorities to remove the pump handle, after which the number of new cholera cases sharply declined.

Legacy

Today, the former Broad Street is known as Broadwick Street, and several commemorations honor Snow’s contribution:

• A pub named after him where the John Snow Society meets.
• A sculpture of the historic pump.
• A plaque on the building that once housed the pump.

Further Resources

• TED Talk: The Ghost Map by Steven Johnson – discusses the impact of Snow’s map on science, cities, and modern societies.
• Wikipedia – John Snow
• Victorian Web – John Snow
• All3dform – “John Snow y el mapa que salvó Londres” (Spanish)
• psanxiao – “El mapa del cólera de John Snow” (Spanish)