Osaka ( ?saka) is a designated city in the Kansai region of Japan. It is the capital city of Osaka Prefecture and the largest component of the Keihanshin Metropolitan Area, the second largest metropolitan area in Japan and among the largest in the world with nearly 19 million inhabitants. Situated at the mouth of the Yodo River on Osaka Bay, Osaka is Japan's third largest city by population after the Tokyo 23 wards and Yokohama, and serves as a major economic hub. Historically a merchant city, Osaka has also been known as the 'nation's kitchen' (ぱ?┮ tenka no daidokoro) and served as a centre for the rice trade during the Edo period.