South Asia is often referred to as a subcontinent because the countries that form South Asia are considered to be part of a large, self-contained landmass within a larger continent. The South Asian subcontinent is also commonly referred to as the Indian Subcontinent.
The reason South Asia is considered part of a self-contained landmass is primarily due to physical geographical features. The first is its division from the rest of the Asian continent by the Himalayas, Karakorum, and Hindu Kush mountain ranges and the second is the Indian Plate, which rises most of the subcontinent above sea level. The Himalayas extend 1,500 miles from the Brahmaputra River to the Karakorum mountains. South Asia is bounded on the west by the Arabian sea, and on the east by the bay of Bengal.
The United Nations geographical region classification officially includes India, Pakistan, Bangladesh, Bhutan, Nepal, Maldives, Afghanistan, Iran and Sri Lanka as countries belonging to South Asia. Some people also include Myanmar and Tibet. These are all countries either directly South of the Himalayas, or adjoining to the west and east. South Asia is home to more than one fifth of the world's population, making it the most populated geographical region in the world.