A new interactive mapping service shows historic immigration patterns in the United States. You can see where different ethnic groups settled. The interactive map is an excellent use of aggregate data from U.S. Census and geographic information systems.
You can see the map at: www.nytimes.com/interactive/2009/03/10/us/20090310-immigration-explorer.html?hp.
My thanks to Liv Marit Haakenstad for telling me about the interactive map.