GIS: Visualizing US Expansion through Post Offices

In an interesting use of GIS, Derek Watkins, a graduate student in geography at the University of Oregon, has created a visualization showing how formal U.S. territorial control expanded in North America from 1700 to 1900, as seen through changes in the spatial distribution of post offices. (The image here is static; follow the link to see the dynamic mapping.) Watkins also points to a similar project showing the growth of newspapers across the United States, 1690-2011, at Stanford's Rural West Initiative.
  Business historians have long been familiar with the importance of the post office in business and economic development. See, for example, Richard R. John, Spreading the News: The American Postal System from Franklin to Morse (1995; pb, 1998); Martin Daunton, The Royal Mail: The History of the Post Office since 1840 (1985); Patricia L. Maclachlin, The People's Post Office: The History and Politics of the Japanese Postal System, 1871-2010 (forthcoming, 2011); and Richard Kielbowicz, News in the Mail: The Press, Post Office, and Public Information, 1700-1860s (1989).