I recently finished reading a wonderful book by Steven Johnson entitled The Ghost Map: The Story of London’s Most Terrifying Epidemic – and How It Changed Science, Cities, and the Modern World. In the summer of 1854 cholera swept through a section of London with unprecedented intensity. At the time, the cause of cholera was unknown and rapidly growing modern cities such as London, with dense populations packed into small areas, were rich breeding grounds for this disease. Most of those who concerned themselves with disease and its cure held tightly to the miasma theory that cholera spread through the air and was associated with the bad smells and the unclean urban environments that produced them. In fact, cholera is a bacterium, which was spreading through the water supply. This book tells the story much as a journalist who witnessed it firsthand would do, but a journalist who had the advantage of hindsight informed by knowledge of modern medicine.
Several people of the time play important roles in this story – none more than John Snow, a medical doctor and research scientist. The ghost map refers to a map that he drew by hand during the process of his investigations, which could clearly demonstrate to anyone with open eyes that the source of the outbreak was the Broad Street well. Despite the evidence that this map displayed, however, the miasma theory of cholera transmission prevailed for several years after the epidemic. Eventually, due largely to the tenacious efforts of John Snow and an unlikely supporter, Reverend Henry Whitehead, the evidence won out and steps were taken to eliminate the conditions in which cholera could spread.
This story is important in the history of data visualization, because it is one of the earliest accounts of how a visual representation of important data was able to bring to light evidence that might have otherwise remained obscured for much longer if relegated to a tabular display. In this case, a picture (in the form of a map with quantitative data) was indeed worth a thousand words and helped to save many thousands of lives.
This is more than the story of a great map, however. It tackles larger issues, such as how new ideas and scientific discoveries become adopted, often against great resistance, even from the intellectuals of the day. John Snow and Henry Whitehead are great role models for all of us who care about discovering and communicating the truth, even when it is unpopular. I recommend this book highly.