The Ganges Basin is a major part of the Ganges-Brahmaputra-Meghna (GBM) basin draining 1,999,000 square kilometres in Tibet, Nepal, India and Bangladesh. To the north, the Himalaya or lower parallel ranges beyond form the Ganges-Brahmaputra divide. On the west the Ganges Basin borders the Indus basin and then the Aravalli ridge. Southern limits are the Vindhyas and Chota Nagpur Plateau. On the east the Ganges merges with the Brahmaputra through a complex system of common distributaries into the Bay of Bengal. Its catchment lies in the states of Uttar Pradesh (294,364 km2), Madhya Pradesh (198,962 km2), Bihar (143,961 km2), Rajasthan (112,490 km2), West Bengal (71,485 km2), Haryana (34,341 km2), Himachal Pradesh (4,317 km2), Delhi, Arunachal Pradesh (1,484 km2), the whole of Bangladesh, Nepal and Bhutan. Several tributaries rise inside Tibet before flowing south through Nepal. The basin has a population of more than 500 million, making it the most populated river basin in the world.