The vast territory of China stretches from north to south for approximately 5,500 km from the central line of the Heilong River at MoheTown in Heilongjiang Province to the Tsengmu Reef in the southernmost part of the South China Sea Islands; and east and west for 5,000 km from the confluence of the Heilong and Wusuli river to the Pamirs in Xinjiang. China's geographical position in eastern Asia and on the western shore of the Pacific enables it to maintain close ties with landlocked neighbours in the west and reach out to other countries across the sea. The abundance of rainfalls precipitated by moist air currents from the sea is a major source of freshwater essential to agriculture development in this country.