Here is a data visualization project I've been working on while learning how to use the Protovis JavaScript Library. This is an example of a Dorling Cartogram that encodes National Park data from 2009. The size of National Park is encoded as the size of the circle and the percentage of attendance as the circle's color. The National Park data comes from The National Park Service Public Use Statistics Reports. My example is based on the Protovis Dorling Cartogram example. The circles are roughly positioned based on the National Park's geographic location. The attendance figures come from the 2009 report.