Tokyo (東京), officially Tokyo Metropolis (東京都 Tōkyō-to), one of the 47 prefectures of Japan, has served as the Japanese Capital City since 1869. As of 2018, the Greater Tokyo Area ranked as the most populous metropolitan area in the world. The historical boundaries of Tokyo City are now occupied by the 23 Special Wards of Tokyo. As of October 1, 2015, the population of Tokyo is estimated to be over 13.4 million, or about 11% of Japan's total population. Tokyo ranks first in the Global Economic Power Index and third in the Global Cities Index.