Many places on Earth can be difficult to live in - some though are extreme. Hot arid areas can be found around the equator and nearby (located at b on the map). This is because the rays of the Sun are more intense and spread over a shorter distance. Cold areas can be found further away from the equator, near the poles. This is because the rays of the Sun are spread out over a greater distance.
In Australia, the semi desert region is created because of a rain shadow (where it doesn't rain). The warm moist air from the Pacific Ocean rises over the Great Dividing Range causing clouds to form (condensation) and rain on the mountains. The air is then dry as it passes through to central Australia.
Polar climates are found where either the Sun's rays are less intense therefore reducing temperature or where altitude (height above sea level) is high. These areas may also be referred to as Tundra or Glacial regions.