South of Tohoku on Honshu island is the Kanto region, the political, cultural, and economic heart of Japan. It centers on Japan's capital city, Tokyo, in east central Honshu. Kanto's main natural feature is the Kanto Plain. Japan's largest flatland, the plain covers 13,000 sq km (5,000 sq mi), or about 40 percent of the Kanto region. Hills and mountains surround the plain on the east, north, and west sides, while the south side opens to the Pacific Ocean. Covering most of the southern part of the plain is the Tokyo metropolitan area, which contains many small cities and satellite towns. Major nearby cities—Yokohama, Chiba, and Kawasaki—merge with Tokyo, creating one large urban-industrial zone. The population of Kanto is the largest of any of Japan's regions. Most of the farms that once covered the Kanto Plain have been replaced by residential, commercial, and industrial construction. The prefectures of Kanagawa, Saitama, Gunma, Tochigi, Ibaraki, Chiba, and the Tokyo Metropolis make up the Kanto region.