Australia, officially the Commonwealth of Australia,[17] is a country comprising the mainland of the Australian continent, the island of Tasmania and numerous smaller islands.[18] Australia has a total area of 7,688,287 km2 (2,968,464 sq mi), making it the sixth-largest country in the world and the largest country by area in Oceania. It is the world's oldest,[19] flattest,[20] and driest inhabited continent,[21][22] with some of the least fertile soils.[23][24] It is a megadiverse country, and its size gives it a wide variety of landscapes and climates including deserts in the interior and tropical rainforests along the coast.