In the essay On the Mode of Communication of Cholera what is the primary technique that author John Snow uses to support his claim that cholera spreads from person to person?

John Snow primarily uses detailed case studies and maps to show the correlation between contaminated water sources and cholera outbreaks, suggesting that the disease spreads through water contaminated with fecal matter. This technique helps him support his claim that cholera is transmitted person to person through contaminated water sources.