I finally got around to reading “The Ghost Map” this week, and I could not put it down.  The combination of epidemiology, politics, governance, superstition, and public health policy really intrigued me.  It is a great explanation of this particular outbreak of cholera on Broad Street in London in 1854.  What I found most interesting about the book, though, was the last chapter.  Here, author Steven Johnson really explains why cities and urban density are critical to our ability to provide public health services to large numbers of people.  Johnson states:

Broad Street marked the first time in history when a reasonable person might have surveyed the state of urban life and come to the conclusion that cities would someday become great conquerors of disease.  Until then, it looked like a losing battle all the way.”

I found this intriguing, because much has been said about the bad side of cities:  urban sprawl, some of them create their own weather systems, they divert massive quantities of water from limited supplies, etc.  Yet, without sewers that separate the water coming in from the water going out, cholera and other waterborne diseases run rampant.  Most importantly, perhaps, Johnson claims that cities are the ultimate tool in the battle against population explosion.  With their easier access to birth control and family planning clinics, increased economic opportunities for women, and expensive real estate, cities “have reversed one of the dominant demographic trends of the last few centuries of life on earth:  the population explosion that has been the subject of countless doomsday scenarios…”

In my learning about migration trends much has been made about the differences between the urban and the rural poor, and how migration trends within countries and between countries differ depending on the urbanization of a particular source or destination.  It seems that according to Johnson, the trend of urbanization must continue if we are to reliably provide essential public serves to the growing number of humans on earth, and that technologies for doing so should focus on this reality.