Houston is the largest city in the state of Texas and the fourth-largest in the United States. As of the 2005 U.S. Census estimate, it had a population of more than 2 million. Houston became the home of the Texas Medical Center, the world’s largest concentration of health care and research institutions, and NASA’s Lyndon B. Johnson Space Center. Houston’s economy has a broad industrial base in the energy, aeronautics, and technology industries and only New York City is home to more Fortune 500 headquarters. Houston is a multicultural city with a large and growing international community. The Museum District is home to many cultural institutions and exhibits, attracting more than 7 million visitors a year. Houston has an active visual and performing arts scene as one of five U.S. cities that offer year-round resident companies in all major performing arts.