The Australian flag features red, white and blue colors. English is the official language, and the currency used to be pounds, shillings and pence. Australia's climate varies regionally from tropical in the north to temperate in the southeast and southwest, with most of the interior being semi-arid desert. The population of around 21.7 million is predominantly descended from European immigrants from the late 18th century onward. Australian culture blends Indigenous traditions with European influences, and celebrations of heritage through various annual arts festivals are popular in major cities.