Osaka (大阪 Ōsaka?) is a city in the Kansai region of Japan's main island of Honshū, a designated city under the Local Autonomy Law, the capital city of Osaka Prefecture and also the biggest part of Keihanshin Area, which is represented by three major cities of Japan, Kyoto, Osaka and Kobe. Located at the mouth of the Yodo River on Osaka Bay, Osaka is the third largest city by population after Tokyo and Yokohama.
For reference, Keihanshin Area is the second largest area in Japan by population and one of the largest metropolitan areas highly ranked in the world, with nearly 18 million people, and by GDP, the second largest area in Japan and the seventh largest area in the world.
Historically the commercial capital of Japan, Osaka functions as one of the command centers for the Japanese economy. The ratio between daytime and night time population is 141%, the highest in Japan, highlighting its status as an economic center. Its nighttime population is 2.6 million, the third in the country, but in daytime the population surges to 3.7 million, second only after Tokyo. Osaka used to be referred to as the "nation's kitchen" (天下の台所 tenka no daidokoro?) in feudal Edo period because it was the centre of trading for rice, creating the first modern future exchange market in the world