Dallas is a major city in Texas and along with Fort Worth, is one of the two urban centers of that ranks fourth in the United States. The city proper ranks ninth in the U.S. and third in Texas after Houston and San Antonio. The city's prominence arose from its historical importance as a center for the oil and cotton industries, and its position along numerous railroad lines. The bulk of the city is in Dallas County, of which it is the county seat. However, sections of the city are located in Collin, Denton, Kaufman, and Rockwall counties. According to the 2010 United States Census, the city had a population of 1,197,816. The United States Census Bureau's estimate for the city's population increased to 1,241,162 as of 2012.The city is the largest economic center of the 12-county metropolitan area, which had a population of 6,810,913 as of July 1, 2013. The metropolitan economy is the sixth largest in the United States, with a 2012 real GDP of $420.34 billion. In 2013 the metropolitan area led the nation with the largest year-over-year increase in employment, and advanced to become the fourth-largest employment center in the nation (behind New York City, Los Angeles and Chicago) with more than three million non-farm jobs. In the latest rankings released in 2013, Dallas was rated as a "beta plus" world city by the Globalization and World Cities Study Group & Network. Dallas is also ranked 14th in world rankings of GDP by the Organisation for Economic Co-operation and Development.