an administrative division of N central Australia, on the Timor and Arafura Seas: the Arunta Desert lies in the east, the Macdonnell Ranges in the south, and Arnhem Land in the north (containing Australia's largest Aboriginal reservation); the Ashmore and Cartier Islands constitute a separate Australian External Territory. Capital: Darwin. Pop: 233 300 (2012 est). Area: 1 347 525 sq km (520 280 sq miles)