Flowing through the city of Guangzhou, the Pearl River is the largest river system in southern China and the third longest one in China, only after the Yangtze River and the Yellow River. The Pearl River Delta is one of the most developed regions in China, of which the area is about 11 thousand square kilometers. Also, it is the biggest urban area in the world in term of size and population. The nine largest cities in the Pearl River Delta have a total population of over 57 million. Since the reform and opening up policy was carried out by the Chinese government in the late 1970s, the Delta has become one of the main economic regions and manufacturing centers in China and all over the world.