Oceania is a geographical region that includes Australasia, Melanesia, Micronesia, and Polynesia. Spanning the Eastern and Western hemispheres, Oceania is estimated to have a land area of 8,525,989 square kilometers (3,291,903 sq mi) and a population of around 44.5 million as of 2021. When compared with the continents, the region of Oceania is the smallest in land area and the second least populated after Antarctica. Its major population centers are Sydney, Melbourne, Brisbane, Perth, Auckland, Adelaide, Honolulu, and Christchurch.