How have cities grown over time? Answers to this important question are provided in visual form via the Lincoln Land Institute's Atlas of Urban Expansion. This resource "provides the geographic and quantitative dimensions of urban expansion and its key attributes in cities the world over." Visitors to the site should start their own exploration by looking at "Making Room for a Planet of Cities," a policy report that examines how the world has become heavily urbanized over the past few decades. Much of the material within the Atlas can be found in the five sections presented on the left toolbar of this site. They include Section 2: A Representative Sample of 30 Cities, 1800-2000 and Section 3: Urban and National Data. The most incredible section here is Section 5: Google Earth Data for the Universe of 3646 Cities. It is a remarkable look at the accuracy of various maps portraying the world's primary cities in a variety of settings. Overall, this site is an invaluable resource for planners, demographers, policy folks, and anyone interested in the urban condition.