Ramba uchinyora ndima iyi - Chiremba wokuBritain John Snow akashandisa mufananidzo wakafanana nowaVoronoi muna 1854 kuratidza kuti ruzhinji rwevanhu vakafa mukubudirira kwecholera muBroad Street
aigara pedyo nepombi yemvura yeBroad Street yakanga yabatwa neutachiona kupfuura imwe pombi yemvura ipi neipi.