Houston anchors Harris County in Southeast Texas, stretching from the Energy Corridor and Katy in the west to Clear Lake and the Port of Houston ship channel in the east, with major employment centers in the Texas Medical Center, downtown's corporate towers, and the petrochemical complexes along the Gulf Coast. The metro area encompasses distinct communities like The Woodlands to the north, Sugar Land and Missouri City to the southwest, and Pearland extending toward Galveston County. As the nation's fourth-largest city, Houston's economy runs on energy sector headquarters, one of the world's largest medical complexes, NASA's Johnson Space Center, and the busiest port in the United States by tonnage, creating demand for services across industrial, professional, and residential sectors throughout Harris, Fort Bend, Montgomery, and Brazoria counties.