1. South Asia is clearly defined physiographically, and much of the realm's boundary is marked by mountains, deserts, and the Indian Ocean.
2. South Asia's great rivers, especially the Ganges, have for tens of thousands of years supported huge population clusters.
3. South Asia, and especially northern India, was the birthplace of major religions that include Hinduism and
4. Due to the realm's natural boundaries, foreign influences in pre-modern South Asia came mainly via a narrow passage in the northwest (Khyber Pass).
5. South Asia covers just over 3 percent of the Earth's land area but contains nearly 26 percent of the world's human population.
6. South Asia's annual monsoon continues to dominate life for hundreds of millions of subsistence and commercial farmers. Failure of the monsoon cycle spells economic crisis.
7. Certain remote areas in the realm's northern mountain perimeter are a dangerous source of friction between India and both Pakistan and China.
8. South Asia is still predominantly rural with hundreds of thousands of small villages; but it is also home to some of the biggest cities in the world.
From Geography: Realms, Regions and Concepts, 13th Edition
by H.J. de Blij, Peter O. Muller