Australia's landmass of 7,617,930 square kilometres (2,941,300 sq mi) is on the Indo-Australian Plate. Surrounded by the Indian and Pacific oceans, it is separated from Asia by the Arafura and Timor seas, with the Coral Sea lying off the Queensland coast, and the Tasman Sea lying between Australia and New Zealand. The world's smallest continent and sixth largest country by total area, Australia—owing to its size and isolation—is often dubbed the "island continent", and is sometimes considered the world's largest island. Australia has 34,218 kilometres (21,262 mi) of coastline (excluding all offshore islands), and claims an extensive Exclusive Economic Zone of 8,148,250 square kilometres (3,146,060 sq mi). This exclusive economic zone does not include the Australian Antarctic Territory. Excluding Macquarie Island, Australia lies between latitudes 9° and 44°S, and longitudes 112° and 154°E.
The Great Barrier Reef, the world's largest coral reef, lies a short distance off the north-east coast and extends for over 2,000 kilometres (1,240 mi). Mount Augustus, claimed to be the world's largest monolith, is located in Western Australia. At 2,228 metres (7,310 ft), Mount Kosciuszko on the Great Dividing Range is the highest mountain on the Australian mainland. Even taller are Mawson Peak (at 2,745 metres or 9,006 feet), on the remote Australian territory of Heard Island, and, in the Australian Antarctic Territory, Mount McClintock and Mount Menzies, at 3,492 metres (11,457 ft) and 3,355 metres (11,007 ft) respectively.
Australia's size gives it a wide variety of landscapes, with subtropical rainforests in the north-east, mountain ranges in the south-east, south-west and east, and dry desert in the centre. It is the flattest continent, with the oldest and least fertile soils; desert or semi-arid land commonly known as the outback makes up by far the largest portion of land. The driest inhabited continent, only its south-east and south-west corners have a temperate climate. The population density, 2.8 inhabitants per square kilometre, is among the lowest in the world, although a large proportion of the population lives along the temperate south-eastern coastline.
Eastern Australia is marked by the Great Dividing Range, which runs parallel to the coast of Queensland, New South Wales and much of Victoria. The name is not strictly accurate, because parts of the range consist of low hills, and the highlands are typically no more than 1,600 metres (5,249 ft) in height. The coastal uplands and a belt of Brigalow grasslands lie between the coast and the mountains, while inland of the dividing range are large areas of grassland. These include the western plains of New South Wales, and the Einasleigh Uplands, Barkly Tableland, and Mulga Lands of inland Queensland. The northernmost point of the east coast is the tropical-rain forested Cape York Peninsula.
The landscapes of the northern part of the country—the Top End and the Gulf Country behind the Gulf of Carpentaria, with their tropical climate—consist of woodland, grassland, and desert. At the north-west corner of the continent are the sandstone cliffs and gorges of The Kimberley, and below that the Pilbara. To the south of these and inland, lie more areas of grassland: the Ord Victoria Plainand the Western Australian Mulga shrublands. At the heart of the country are the uplands of central Australia; prominent features of the centre and south include the inland Simpson, Tirari and Sturt Stony, Gibson, Great Sandy, Tanami, and Great Victoria deserts, with the famous Nullarbor Plain on the southern coast.
The climate of Australia is significantly influenced by ocean currents, including the Indian Ocean Dipole and the El Niño–Southern Oscillation, which is correlated with periodic drought, and the seasonal tropical low-pressure system that produces cyclones in northern Australia. These factors cause rainfall to vary markedly from year to year. Much of the northern part of the country has a tropical, predominantly summer-rainfall (monsoon) climate. The southwest corner of the country has a Mediterranean climate. Much of the southeast (including Tasmania) is temperate.
Although most of Australia is semi-arid or desert, it includes a diverse range of habitats from alpine heaths to tropical rainforests, and is recognised as a megadiverse country. The fungi typify that diversity; the total number that occur in Australia, including those not yet discovered, has been estimated at around 250,000 species, of which roughly 5% have been described. Because of the continent's great age, extremely variable weather patterns, and long-term geographic isolation, much of Australia's biota is unique and diverse. Approximately 85% of flowering plants, 84% of mammals, more than 45% of birds, and 89% of in-shore, temperate-zone fish are endemic. Australia has the greatest number of reptiles of any country, with 755 species.
Australian forests are mostly made up of evergreen species, particularly eucalyptus trees in the less arid regions, wattles replace them in drier regions and deserts as the most dominant species. Among well-known Australian animals are the monotremes (the platypusand echidna); a host of marsupials, including the kangaroo, koala, and wombat, and birds such as the emu and the kookaburra. Australia is home to many dangerous animals including some of the most venomous snakes in the world. Many animal and plant species became extinct soon after first human settlement.
Climate change has become an increasing concern in Australia in recent years, and protection of the environment is a major political issue.
Australia has six states—New South Wales (NSW), Queensland (QLD), South Australia (SA), Tasmania (TAS),Victoria (VIC) and Western Australia (WA)—and two major mainland territories—the Australian Capital Territory (ACT) and the Northern Territory (NT). In most respects these two territories function as states, but the Commonwealth Parliament can override any legislation of their parliaments. By contrast, federal legislation overrides state legislation only in areas that are set out in Section 51 of the Australian Constitution; state parliaments retain all residual legislative powers, including those over schools, state police, the state judiciary, roads, public transport and local government, since these do not fall under the provisions listed in Section 51.
Each state and major mainland territory has its own parliament—unicameral in the Northern Territory, the ACT and Queensland—and bicameral in the other states. The head of the government in each state is the Premier and in each territory the Chief Minister.