Tokyo, officially Tokyo Metropolis, is one of the 47 prefectures of Japan and located on the eastern side of the main island Honshū. The twenty-three special wards of Tokyo, each governed as a city, cover the area that was once the city of Tokyo in the eastern part of the prefecture, and total over 8 million people. The population of the prefecture exceeds 12 million. Tokyo is the seat of the Japanese government and the Imperial Palace, and the home of the Japanese Imperial Family. The name "Tokyo" literally means eastern capital. Tokyo has enacted a measure to cut greenhouse gases. Governor Shintaro Ishihara created Japan's first emissions cap system, aiming to reduce greenhouse gas emission by a total of 25 percent by 2020 from the 2000 level. Tokyo is one of the three world finance "command centers", along with New York City and London. Tokyo has the largest metropolitan economy in the world. Tokyo is Japan's largest domestic and international hub for rail, ground, and air transportation. Public transportation within Tokyo is dominated by an extensive network of clean and efficient trains and subways run by a variety of operators, with buses, monorails and trams playing a secondary feeder role. Tokyo has many museums. In Ueno Park are four national museums: Tokyo National Museum, the country's largest museum and specializing in traditional Japanese art; the National Museum of Western Art; and the Tokyo National Museum of Modern Art, with its collections of Japanese modern art as well as over 40,000 Japanese and foreign films.