Baku (, ), sometimes spelled as Baki or Bakou, is the capital and largest city of Azerbaijan, as well as the largest city on the Caspian Sea and of the Caucasus region. It is located on the southern shore of the Absheron Peninsula, which projects into the Caspian Sea. The city consists of two principal parts: the downtown and the old Inner City (21.5 ha). Baku's urban population at the beginning of 2009 was estimated at just over two million people. Officially, about 25 percent of all inhabitants of the country live in the metropolitan city area of Baku.