Guangzhou, known historically as Canton or, less commonly as Kwangchow, is the capital and largest city of Guangdong province, People's Republic of China. Located on the Pearl River, about 120 km north-northwest of Hong Kong and north-northeast of Macau, Guangzhou is a key national transportation hub and trading port. One of the five National Central Cities, it holds sub-provincial administrative status.Guangzhou is the third largest Chinese city and southern China's largest city. As of the 2010 census, the city had a population of 12.78 million. Some estimates place the population of the entire Pearl River Delta Mega City built up area as high as 40 million including Shenzhen, Dongguan and most parts of Foshan, Jiangmen, Zhongshan and a small part of Huizhou adjoining Dongguan and Shenzhen, with an area of about 20,000 square kilometres.In 2008 Guangzhou was identified as a Beta World City by the global city index produced by the GaWC, the Globalization and World Cities Research Network.