After the spread of cholera in 1854, John Snow decided to map the deaths around London’s Broad Street. The fact of linking the reported cases after the outbreak to the location of the dead’s houses proved that they had a strong link to a public drinking water pump. Those who had used that pump had a higher chance of contracting the disease. This primitive spatial analysis took to pieces the theory that cholera was connected to pestilent air rather than drinking waters infected by sewage. And as a matter of fact, it led to stop the practice of simply draining human wastewaters into the River Thames, which was to be drunk later by citizens.