Minnesota is located in the northern part of the United States, close to the Great Lakes, so there are many inland lakes in the state, and water transportation is relatively developed. The state has a land area of 219,000 square kilometers and a population of 5.16 million. The capital of the state is Saint Paul, a famous port city. Minnesota's main economy is the development of real estate and rental markets, followed by manufacturing, and financial and insurance industries are also relatively developed. The largest city in the state is Minneapolis, and other more important cities are: Duluth, Santa Cruz, Mancado, Rochester and Bloomington. Minnesota is home to St. Paul International Airport (MSP), which is a transit center for Northwest Airlines and a transit center for Delta Air Lines. Therefore, the transportation here is very convenient, and many goods are transported out by the river through the inner port. The establishment of the air terminal has allowed the freight business in Minnesota to develop rapidly. The area code for Minnesota is: 218 - 320 - 507 - 612 - 651 - 763 - 952 and the abbreviated ZIP code is: MN. The zip code references for major cities are as follows: 55101 for Saint Paul, 55401 for Minneapolis, and 55801 for Duluth.