 Australia 's size gives it a wide variety of landscapes , with tropical 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 , its annual rainfall averaged over continental area is less than 500 mm . 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 . 
