Maryland is located in the northeastern region of the United States, near the Chesapeake Bay in the Atlantic Ocean. The state has an area of 32,000 square kilometers and a population of 5.77 million. The state's capital is Annapolis. Maryland has lush forest vegetation and abundant forest resources, so a large amount of wood is produced, mainly hardwood. Second, there are coal resources. The state's manufacturing industry is also very developed, producing trucks, passenger cars, railway equipment, aircraft components, aircraft control systems, and more. In recent years, industrial equipment and computers have been exported. Maryland's zip code is MD, the area code is 240 – 301 – 410 – 443, the main city zip code is: Annapolis zip code is 21001-21412; Baltimore zip code is 21201-21298; Rockville zip code is 21201-21298 ) in 20847-20857.