Australia is the fifth and smallest continent. It covers approximately 7.700.000 square kilometres, the mainland is almost 4.000 kilometres from west to east and over 3.000 kilometres from north to south. Most of the land is very flat. The very old Western Plateau is generally only 300 metres above sea-level and is mostly desert or semi-desert. In general Austrlia's climate has a mild drought or dry period every five years and a bad one evrey ten. One example is Central Australia which went without rain for seven years in 1970s. therefore, although the soil may be fertile in the inland , little or no water makes it almost impossible for people to live there and use the land. Much of the water that has managed to reach these dry areas over hundreds of years and run into the lake system has brought salt to the surface . the heat evaporates the water. As the lakes dry out the water just below the surface rises because of the heat and also evaporates on the surface bringing up salts from the soils. The Western Plateau contains many salt lakes . Lake Eyre, the largest , covers an area over 9.000 square kilometres and as the lowest is 16 metres below sealevel. It is the drainage basin of the inland river system that confused the early settlers who thought the area would be well supplied with fresh water. Due to these conditions there are only the two large settlements of Darwin in the north and alice springs in the centre.
The Tropics are in the north and have wet and dry seasons controlled by the monsoons, wet seasonal rains blowing south from the equator . the wet seasons normally starts in November and continues to April. Rainfalls are heavy and continual, often washing out roads and making travel across the country impossible. Planes can only land on sealed or concrete airfields and not on any flat area of cleared ground. Thick, tall tropical rain forest still covers large areas of the north-east. Only 3% of the population live in the north, again because of the climate.
The Great Dividing Range runs along the eats coast from north to south. Its name describes what it does - to divide the continent into two main areas. West of the Great dividing Range the yearly rainfall drops until the desert areas are reached. About one third of the continent receives under 25 cm of rain each year and another third between 25 and 50 cm a year. Australia is the driest continent on earth. The Great Dividing Range has Australia's highest mountain, Mount Kosciusko , in the "Australian Alps". The Australian Alps are relatively low by world standards and were covered with glaciers. They are steep , rugged and covered with native eucalyptus forest.
Most of the population live in the east and south-east coastal areas, especially around the cities of Melbourne , Sydney Adelaide and Briusbane. Other areas where more people live are Tasmania which is cut off from the mainland by Bass Strait. It has a much milder climate with snow each winter and about 3% of the population live there. Around 17% of the Australian population live on the south-west coast around Perth, where the climate is warm, but pleasant and rainfall is enough to support farms and a large city.