mostly low plateau with deserts, rangelands and a fertile plain in the southeast; mountain ranges in the east and south-east. The geography of Australia encompasses a wide variety of biogeographic regions being the world's smallest continent but the sixth-largest country in the world.Australia, Zealandia, and New Guinea are continental islands. These three regions share some physical features. All three have mountain ranges or highlands—the Great Dividing Range in Australia; the North Island Volcanic Plateau and Southern Alps in New Zealand; and the New Guinea Highlands in Papua New Guinea.Australia is the smallest of the world's continents. It is also the lowest, the flattest and (apart from Antarctica) the driest. The highest point on the Australian mainland is Mount Kosciuszko, New South Wales, at 2228 metres above sea level.