Australia has diverse landscapes ranging from desert in the interior Outback to coastal plains. It is surrounded by oceans and home to the Great Barrier Reef, the world's largest coral reef system. The flag represents Australia's British colonial history and Southern Hemisphere location, with references to the Union Jack and Southern Cross constellation. Popular sports include football, cricket, rugby and netball, and exotic endemic mammals include the platypus, kangaroo, wallaby, koala, numbat and dingo.