Detroit is the center of a three-county urban area (population 3,734,090, area of 1,337 square miles (3,460 km2), a 2010 United States Census) six-county metropolitan statistical area (2010 Census population of 4,296,250, area of 3,913 square miles [10,130 km2]), and a nine-county Combined Statistical Area (2010 Census population of 5,218,852, area of 5,814 square miles [15,060 km2]). How many square miles is is Detroit's urban area?