Kanto Region Tokyo Prefecture A prefecture of Japan on Honshu Island. Unique among the prefectures, provides certain municipal services characteristic of a city, The mainland portion of Tokyo lies northwest of Tokyo Bay and measures about 90 km east to west and 25 km north to south. Chiba Prefecture borders it to the east, Yamanashi to the west, Kanagawa to the south, and Saitama to the north. Mainland Tokyo is further subdivided into the special wards (occupying the eastern half) and the Tama area stretching westwards.