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. 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. The People's Republic of China has an area of about 9,600,000 km2 (3,700,000 sq mi). The exact land area is sometimes challenged by border disputes, most notably about Taiwan, Aksai Chin, the Trans-Karakoram Tract, and South Tibet. The area of the People's Republic of China is 9,596,960 km2 (3,705,410 sq mi) according to the CIA's The World Factbook. The People's Republic of China is either the third or fourth-largest country in the world, being either slightly larger or slightly smaller than the United States, depending on how the area of the United States is measured. Both countries are smaller than Russia and Canada and larger than Brazil. Source: Wikipedia (en)