gis analyses of dr snows map
Snow’s map, demonstrating the cholera deaths clustered around the Broad Street well, provided strong evidence in support of his theory that cholera was a water-borne disease. Snow drew Thiessen polygons around the wells, defining straight-line least-distance service areas for each. Each Thiessen polygons is comprised of boundary segments that perpendicularly bisect line segments drawn between the point it contains and adjacent points. A large majority of the cholera deaths fell within the Thiessen polygon surrounding the Broad Street pump, amd a large portion of the remaining deaths were on the Broad Street side of the polygon surrouding the bad-tasting Carnaby Street well.