<P> The country's longest and most important waterway, the Yangtze River, is navigable for the majority of its length and has a vast hydroelectric potential . Rising on the Qingzang Plateau, the Yangtze River traverses 6,300 km (3,900 mi) through the heart of the country, draining an area of 1,800,000 km (690,000 sq mi) before emptying into the East China Sea . Roughly 300 million people live along its middle and lower reaches . The area is a large producer of rice and wheat . The Sichuan Basin, due to its mild, humid climate and long growing season, produces a variety of crops . It is a leading silk - producing area and an important industrial region with substantial mineral resources . </P> <P> The Nanling Mountains, the southernmost of the east--west mountain ranges, overlook areas in China with a tropical climate . The climate allows two crops of rice to be grown per year . Southeast of the mountains lies a coastal, hilly region of small deltas and narrow valley plains . The drainage area of the Pearl River and its associated network of rivers occupies much of the region to the south . West of the Nanling, the Yunnan - Guizhou Plateau rises in two steps, averaging 1,200 and 1,800 m in elevation, respectively, toward the precipitous mountain regions of the eastern Qingzang Plateau . </P> <P> China has substantial mineral reserves and is the world's largest producer of antimony, natural graphite, tungsten, and zinc . Other major minerals are aluminum, bauxite, coal, crude petroleum, diamonds, gold, iron ore, lead, magnetite, manganese, mercury, molybdenum, natural gas, phosphate rock, tin, uranium, and vanadium . China's hydropower potential is the largest in the world . </P> <P> Based on 2005 estimates, 14.86% (about 1,400,000 km (540,000 sq mi)) of China's total land area is arable . About 1.3% (some 116,580 km2) is planted to permanent crops and the rest planted to temporary crops . With comparatively little land planted to permanent crops, intensive agricultural techniques are used to reap harvests that are sufficient to feed the world's largest population and still have surplus for export . An estimated 544,784 km2 of land were irrigated in 2004 . 42.9% of total land area was used as pasture, and 17.5% was forest . </P>

How does china's physical features affect the population