Tokyo (東京 Tōkyō?, "Eastern Capital"), officially Tokyo Metropolis (東京都 Tōkyō-to?), is one of the 47 prefectures of Japan, and is both the capital and largest city of Japan. The Greater Tokyo Area is the most populous metropolitan area in the world. It is the seat of the Emperor of Japan and the Japanese government. Tokyo is in the Kantō region on the southeastern side of the main island Honshu and includes the Izu Islands and Ogasawara Islands. Formerly known as Edo, it has been the de facto seat of government since 1603 when Shogun Tokugawa Ieyasu made the city his headquarters. It officially became the capital after Emperor Meiji moved his seat to the city from the old capital of Kyoto in 1868; at that time Edo was renamed Tokyo. Tokyo Metropolis was 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?). It is also where Chobits takes place. It is home to advanced technology, known as Persocoms.
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% by 2020 from the 2000 level. Tokyo is an example of an urban heat island, and the phenomenon is especially serious in its special wards. According to the Tokyo Metropolitan Government, the annual mean temperature has increased by about 3 °C (5.4 °F) over the past 100 years. Tokyo has been cited as a "convincing example of the relationship between urban growth and climate."
In 2006, Tokyo enacted the "10 Year Project for Green Tokyo" to be realised by 2016. It set a goal of increasing roadside trees in Tokyo to 1 million (from 480,000), and adding 1,000 ha of green space 88 of which will be a new park named "Umi no Mori" (sea forest) which will be on a reclaimed island in Tokyo Bay which used to be a landfill. From 2007 to 2010 436 ha of the planned 1,000 ha of green space was created and 220,000 trees were planted bringing the total to 700,000. By 2014 road side trees in Tokyo will increase to 950,000 and a further 300 ha of green space will be added.