Farmlands, wetlands, forests, and deserts that composed the American landscape in the early twentieth century have frequently been transformed during the past thirty years into mushrooming metropolitan areas as urbanization spreads across the country. Many metropolitan areas in the United States are growing at extraordinary rates. "Urban growth is a vital issue that requires our careful attention from local to global scales," said Barbara Ryan, USGS Associate Director of Geography. "It is not until we begin to take a broad census of the land itself—tracking land scapes from a spatial perspective in a time scale of decades that we can grasp the scale of the changes that have already occurred and predict the impact of changes to come." On average, between 1984 and 2004, Atlanta, Boston, Chicago, Denver, Houston, Las Vegas, Memphis, Minneapolis-St. Paul, Orlando, Phoenix, Pittsburgh, Raleigh-Durham, Reno-Sparks, Sacra memo, Seattle-Tacoma, and Tampa-St. Petersburg averaged 173 square miles of additional urban land over the two de-cades, with Houston, Orlando, and Atlanta as the top three regions by area. The growth leaders by percentage change were Las Vegas (193 percent), Orlando (157 percent), and Phoenix (103 percent).