Most people think of urban sprawl as the construction of roads and buildings at a rate that exceeds population growth. Phoenix, Arizona, however, offers a contrasting model of sprawl. Its metropolitan area has grown more than 300 percent in recent decades, but its population has grown even faster. Since the mid-1980’s, the city’s population density has increased as people continue to move to the region even as the urban area’s boundaries have grown more slowly. This trend is by necessity, since the water supply cannot feed an ever-expanding metropolitan area.