Snow takes center stage for much of the narrative early on as he puts forth, against considerable resistance from the medical and bureaucratic establishment, the innovative theory that cholera was spread through unhygienic water rather than through miasma. It was a tough sell, however, but in concert with Whitehead and his “reputation for sociability and kindness” — once the clergyman too was convinced of Snow’s waterborne theory — more doors opened to further data, residents, and governing boards.

Consequently, with better access to and vital information from the right people, the gaps in the “ghost map” were filled in, not only completing in full the charting and dimensions of the outbreak, but also more pragmatically the plotting of a course for better public health. As organizational documents, the maps were invaluable in helping persuade the powers-that-be of the validity of the medical treatments based on Dr. Snow's waterborne theories. And the utmost upshot came when officials were begrudgingly persuaded to remove the Broad Street pump handle, a decision that saved hundreds, maybe thousands of lives.

Encouraged by such short-term successes, Dr. Snow’s science-centered approach in battling cholera sets a sensible precedent for long-run courses of action as the ensuing years saw public officials take steps to prevent more epidemics by building, for example, the vast sewer system that continues to function in London today. Furthermore, as Johnson reveals his compelling and well-considered and comprehensive work, Snow's charting of sanitation and disease control offers lessons for modern city planners, public officials, and physicians, suggesting approaches for the management of urban sprawl, environmental crises, and the threat of bio-terrorism.

In regards, then, to the evolution of public health, The Ghost Map truly marks “a case study in how change happens in human society, the turbulent way in which wrong or ineffectual ideas are overthrown by better ones.”