In 1854, he played a key role in stopping a cholera outbreak which had killed hundreds of people within a few weeks.
Ah, so it’s not that other John Snow you’re named after.
John Snow built a detailed map of all the households where people died, and came to the conclusion that the fault was one public water pump that all the victims had used.
Back than as today, collecting quality data was the hardest part.
However, the big insight wasn’t the pump but the fact that cholera was a waterborne disease.
This was a new discovery at the time.
Today we call this “data mining for actionable insights”.