Metropolitan areas in the United States are growing at unprecedented rates, creating extensive urban landscapes. Many of the farmlands, wetlands, forests, and deserts that formed the America of 1900 have been transformed during the past 100 years into human settlements. Almost everyone has seen these changes to their local environment but without a clear understanding of their impacts. It is not until we study these landscapes from a spatial perspective and the time scale of decades that we can begin to measure the changes that have occurred and predict the impact of changes to come.