Sydney is the capital city of the state of New South Wales and the most populous city in Australia. Located on Australia's east coast, the metropolis surrounds Sydney Harbour and extends about 80 km (50 mi) from the Pacific Ocean in the east to the Blue Mountains in the west, and about 80 km (50 mi) from Ku-ring-gai Chase National Park and the Hawkesbury River in the north and north-west, to the Royal National Park and Macarthur in the south and south-west. Greater Sydney consists of 658 suburbs, spread across 33 local government areas. The city's nicknames include the Emerald City and the Harbour City. The New South Wales Legislative Council became a semi-elected body in 1842. Sydney was declared a city the same year, and a governing council established, elected on a restrictive property franchise. When the six colonies federated on 1 January 1901, Sydney became the capital of the State of New South Wales.

Sydney is a coastal basin with the Tasman Sea to the east, the Blue Mountains to the west, the Hawkesbury River to the north, and the Woronora Plateau to the south. Sydney spans two geographic regions. The Cumberland Plain lies to the south and west of the Harbour and is relatively flat. The Hornsby Plateau is located to the north and is dissected by steep valleys. The flat areas of the south were the first to be developed; it was not until the construction of the Sydney Harbour Bridge that the northern reaches became more heavily populated. Seventy surf beaches can be found along its coastline, with Bondi Beach being the most famous. The Nepean River wraps around the western edge of the city and becomes the Hawkesbury River before reaching Broken Bay. Most of Sydney's water storages can be found on tributaries of the Nepean River. The Parramatta River is mostly industrial and drains a large area of Sydney's western suburbs into Port Jackson. The southern parts of the city are drained by the Georges River and the Cooks River into Botany Bay.