How did john snow use maps to solve the 1854 cholera epidemic? what did his maps tell hin was causing it?

Here's what I get  

Explanation:

John Snow mapped the cholera cases, representing each death as a bar.

His maps showed that many cases were clustered around a public water pump on Broad St. that was close to an old cesspit. The local council eventually disabled the pump by removing its handle.

The diagram below shows his original map overlaid by modern data points. The blue arrow points to the location of the pump.