Dalls is the fourth most populous metropolitan area in the United States ,the city is the largest economic center of the 12-county Dallas–Fort Worth metroplex metropolitan area (commonly referred to as DFW), which had a population of 7,246,231 as of July 1, 2016, representing growth in excess of 807,000 people since the 2010 census, the second largest population increase in the U.S. after Houston. Located in North Texas, Dallas is the main core of the largest metropolitan area in the South and the largest inland metropolitan area in the United States that lacks any navigable link to the sea.Dallas and nearby Fort Worth were developed due to the construction of major railroad lines through the area allowing access to cotton, cattle, and later oil in North and East Texas. The construction of the Interstate Highway System reinforced Dallas' prominence as a transportation hub with four major interstate highways converging in the city, and a fifth interstate loop around it. Dallas developed as a strong industrial and financial center, and a major inland port, due to the convergence of major railroad lines, interstate highways, and the construction of Dallas/Fort worth International Airport, one of the largest and busiest airports in the world