Chongqing (simplifie Chinese: 重庆; traditional Chinese: 重慶; pinyin: Chóngqìng; Postal map spelling: Chungking; Wade-Giles: Ch'ung-ch'ing) is the largest and most populous of the People's Republic of China's four provincial-level municipalities, and the only one in the less densely populated western region of China. Formerly (until 14 March 1997) a sub-provincial city within Sichuan Province, the municipality of Chongqing has a registered population of 31,442,300 (2005). The boundaries of Chongqing municipality reach much further into the city's hinterland than the boundaries of the other three provincial level municipalities (Beijing, Shanghai and Tianjin), and much of the municipality, which spans over 20 million acres (80,000 sq. km.) is rural. The population of the urban area of Chongqing proper was 4.1 million in 2005 although this figure is disputed owing to difficulties as to where the urban area of Chongqing begins and ends.