The Ghost Map: The Story of London's Most Terrifying Epidemic--and How It Changed Science, Cities, and the Modern World

by Steven Johnson

the real innovation lay in the data that generated that diagram, and in the investigation that compiled the data in the first place. Snow’s Broad Street map was a bird’s eye view, but it was drawn from true street-level knowledge. The data that it sketched out in graphic form was a direct reflection of the ordinary lives of the ordinary people who made up the neighborhood. Any engineer could have crafted a dot map from William Farr’s Weekly Returns. But the Snow map drew on a deeper, more intimate, source: two Soho residents talking to their neighbors, walking the streets together, sharing information about their daily routines, and tracking down the long-departed émigrés. Neighborhood demographics had been projected onto maps before, of course, but invariably the projections involved the official interventions of the census takers or the Board of Health. Snow’s map—with Whitehead’s local knowledge animating it—was something else entirely: a neighborhood representing itself, turning its own patterns into a deeper truth by plotting them on a map. The map is a brilliant work of information design and epidemiology, no doubt. But it is also an emblem of a certain kind of community—the densely intertwined lives of a metropolitan neighborhood—an emblem that, paradoxically, was made possible by a savage attack on that community.