Oklahoma is located in the south-central part of the United States, with a land area of 181,089 square kilometers and a population of 3.57 million. The capital is Oklahoma City, with a population of 530,000. Other major cities include: Tulsa, Lorton, Norman City and Midwest City. The economy of Oklahoma is mainly based on agriculture and manufacturing, and the main transportation is still mainly air transportation. There are material distribution centers and inland water transportation. The more important airports are: Will Rogers World Airport. Oklahoma's abbreviated zip code is OK, the area code is 405 - 580 - 918, and the main city zip code is: Oklahoma City 73101-73199. The postal code for Tulsa is 74101-74194. Lawton's zip code is 73504-73507. The postcode for Norman City is 73019-73072.