The map above show Snow's first map, with the bars indicating the number of deaths per household. While Snow himself made edits to this map after its original publication, further studies of the cholera outbreak reveal that Snow's original hypothesis may not have been correct. It seems to be that the one who really discovered the cause and transmission of the cholera outbreak was actually Edmund Cooper, who created a map prior to Snow's, showing the households in which death occurred, and the number of deaths per household. Cooper's map was based not on the spread of cholera through the water pumps, but rather through the link between the sewage system and the cholera outbreak.
If we think in terms of GIS, merely finding and mapping information gives the appearance of data, but it does not actually tell us the cause of an outbreak. If this is true, we can then conclude that Snow's maps were misleading in educating the public on the cholera outbreak, and that it was Cooper who discovered the true cause of the London cholera outbreak.
Brody, H., Rip, M. R., Vinten-Johansen, P., Paneth, N., & Rachman, S. (2000). Map-making and myth-making in Broad Street: the London cholera epidemic, 1854. The Lancet, 356(9223), 64-68. doi:10.1016/s0140-6736(00)02442-9