Iran, also known as Persia and officially the Islamic Republic of Iran (IRI), is a country in West Asia. It is bordered by Iraq to the west and Turkey to the northwest, Azerbaijan, Armenia, the Caspian Sea and Turkmenistan to the north, Afghanistan to the east, Pakistan to the southeast, the Gulf of Oman and the Persian Gulf to the south. With a mostly Persian population of almost 90 million in an area of 1,648,195 km2, Iran ranks 17th globally in both geographic size and population. It is the sixth-largest country entirely in Asia, the second-largest in West Asia, and one of the world's most mountainous countries. Officially a Islamic Republic, Iran has a Muslim-majority population. The country is divided into five regions with 31 provinces. The nation's capital and most populous city is Tehran, with around 16 million people in its metropolitan area, other major cities include Mashhad, Isfahan, Karaj, and Shiraz.