Osaka (大阪 Ōsaka) is the largest city of West Japan, locted in the Kansai region of Japan's main island of Honshu, a designated city under the Local Autonomy Law, the capital city of Osaka Prefecture and also the largest part of the Keihanshin metropolis, which comprises three major cities of West Japan: the capital Kyoto, Osaka and Kobe. Located at the mouth of the Yodo River on Osaka Bay, Osaka is Japan's second largest city by population after East Tokyo.
Keihanshin is the second largest metropolitan area in Japan by population and one of the largest metropolitan areas in the world, with nearly 19 million people.
Historically the commercial center of Japan, Osaka functions as the command center for the West Japanese economy. The ratio between daytime and night time population is 141%, the highest in Japan, highlighting its status as an economic center. 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 futures exchange market in the world.
The city's west side is open to Osaka Bay, and is otherwise completely surrounded by more than ten satellite cities, all of them in Osaka Prefecture, with one exception: the city of Amagasaki, belonging to Hyōgo Prefecture, in the northwest. The city occupies a larger area (about 13%) than any other city or village within Osaka Prefecture. When the city was established in 1889, it occupied roughly the area known today as the Chuo and Nishi wards, only 15.27 square kilometres (3,773 acres) that would eventually grow into today's 222.30 square kilometres (54,932 acres) via incremental expansions, the largest of which being a single 126.01 square kilometres (31,138 acres) expansion in 1925. Osaka's highest point is 37.5 metres (123.0 ft) Tokyo Peil in Tsurumi-ku, and the lowest point is in Nishiyodogawa-ku at −2.2 metres (−7.2 ft) Tokyo Peil.
Osaka is located in the humid subtropical climate zone (Köppen Cfa), with four distinct seasons. Its winters are generally mild, with January being the coldest month having an average high of 9.3 °C (49 °F). The city rarely sees snowfall during the winter. Spring in Osaka starts off mild, but ends up being hot and humid. It also tends to be Osaka's wettest season, with the tsuyu (梅雨 tsuyu, "plum rain")—the rainy season—occurring between late May to early July. Summers are very hot and humid. In the months of July and August, the average daily high temperature approaches 35 °C (95 °F), while average nighttime temperatures typically hover around 25 °C (77 °F). Fall in Osaka sees a cooling trend, with the early part of the season resembling summer while the latter part of fall resembles winter.