Tibet is a plateau region in Central Asia an the home to the indigenous Tibetan people. With an average elevation of 4,900 metres (16,000 ft.), it is the highest region on Earth and is commonly referred to as the "Roof of the World." Geographically, UNESCO and Encyclopædia Britannica consider Tibet to be part of Central Asia, while several academic organizations consider it part of South Asia. Tibet was once an independent kingdom but today is part of the People's Republic of China (PRC) (with a small part, depending on definitions, controlled by India). As an exclusive mandate, Tibet is also officially claimed by the Republic of China (Taiwan). However, the government of the People's Republic of China and the Government of Tibet in Exile still disagree over when Tibet became a part of China, and whether the incorporation into China is legitimate according to international law.