China has great physical diversity. The eastern plains and southern coasts of the country consist of fertile lowlands and foothills. They are the location of most of China's agricultural output and human population. The southern areas of the country (south of the Yangtze River) consist of hilly and mountainous terrain. The west and north of the country are dominated by sunken basins (such as the Gobi and the Taklamakan), rolling plateaus, and towering massifs. It contains part of the highest tableland on earth, the Tibetan Plateau, and has much lower agricultural potential and population. Traditionally, the Chinese population centered on the Chinese central plain and oriented itself toward its own enormous inland market, developing as an imperial power whose center lay in the middle and lower reaches of the Yellow River on the northern plains.[citation needed] More recently, the 18,000 km (11,000 mi) coastline has been used extensively for export-oriented trade, causing the coastal provinces to become the leading economic center. (Source: Wikipedia.org, CC BY-SA)