Tokyo (東京 Tōkyō, , ), officially Tokyo Metropolis (東京都 Tōkyō-to), is one of the 47 prefectures of Japan. It has served as the Japanese capital since 1869, its urban area housing the Emperor of Japan and the Japanese government. Tokyo forms part of the Kantō region on the southeastern side of Japan's main island, Honshu, and includes the Izu Islands and Ogasawara Islands. Tokyo was formerly named Edo when Shōgun Tokugawa Ieyasu made the city his headquarters in 1603. It became the capital after Emperor Meiji moved his seat to the city from Kyoto in 1868; at that time Edo was renamed Tokyo. The Tokyo Metropolis formed in 1943 from the merger of the former Tokyo Prefecture (東京府 Tōkyō-fu) and the city of Tokyo (東京市 Tōkyō-shi). Tokyo is often referred to as a city but is officially known and governed as a "metropolitan prefecture", which differs from and combines elements of a city and a prefecture, a characteristic unique to Tokyo.