topography

Sydney's urban area is in a coastal basin, which is bordered by the Pacific Ocean to the East, the Blue Mountains to the West, the Hawkesbury River to the North and the Royal National Park to the South. It lies on a submergent coastline, where the ocean level has risen to flood deep river valleys (ria) carved in the hawkesbury sandstone. Port Jackson, better known as Sydney Harbour, is one such ria and is the largest natural harbour in the world.[23] The Sydney area is not affected by significant earthquakes. The urban area has around 70 harbour and ocean beaches, including the famous Bondi Beach. Sydney's urban area covers 1,687 km2 (651 sq mi) as at 2001.[24] The Sydney Statistical Division, used for census data, is the unofficial metropolitan area [25] and covers 12,145 km2 (4,689 sq mi).[26] This area includes the Central Coast, the Blue Mountains, and national parks and other unurbanised land. This makes Sydney the third largest urban agglomeration in the world (with a population of over 3 million) behind Brasília (14,400 km²) and Tokyo (13,500 km²).[27]
Geographically, Sydney lies over two regions: the Cumberland Plain, a relatively flat region lying to the south and west of the harbour, and the Hornsby Plateau, a sandstone plateau lying mainly to the north of the harbour and dissected by steep valleys. The parts of the city with the oldest European development are located in the flat areas south of the harbour. The North Shore was slower to develop because of its hilly topography and lack of access across the harbour. The Sydney Harbour Bridge was opened in 1932 and linked the North Shore to the rest of the city.