Sydney, situated on a submergent coastline, is defined by its striking geography and natural features. The city is bordered by the Tasman Sea to the east, the majestic Blue Mountains to the west, the Hawkesbury River to the north, and the Woronora Plateau to the south. This coastal basin is characterized by deep rias, a testament to the area’s geological history.

Sydney spans two major geographic regions: the relatively flat Cumberland Plain to the south and west, and the rugged Hornsby Plateau to the north, marked by steep valleys. The development of Sydney progressed from the flatter areas to the north, which saw significant growth after the construction of the Sydney Harbour Bridge. The coastline is home to 70 surf beaches, with Bondi Beach being the most iconic.

The city is crisscrossed by several rivers, including the Nepean River, which transforms into the Hawkesbury River before reaching Broken Bay. The Parramatta River, primarily industrial, drains much of Sydney's western suburbs into Port Jackson. Other waterways, such as the Georges River and Cooks River, flow into Botany Bay, enhancing Sydney's intricate drainage system.

Defining the boundaries of Sydney can be complex; the Greater Sydney area encompasses approximately 12,369 square kilometers, including various local government regions. The City of Sydney, a smaller area, covers about 26 square kilometers from Garden Island to Bicentennial Park.

Geologically, Sydney is predominantly composed of Triassic sandstone, shaped by ancient river deltas and coastal processes. The region features two main soil types: sandy soils from the Hawkesbury sandstone and clay soils from shales and volcanic rock. The area’s unique geology is exemplified by the Wianamatta shale, which underlies much of western Sydney.

Ecologically, Sydney supports a variety of plant communities, primarily grassy woodlands and dry sclerophyll forests, home to native eucalyptus and other flora. Critically endangered ecosystems, such as the Cumberland Plain Woodland and Eastern Suburbs Banksia Scrub, contribute to Sydney's rich biodiversity. The city is also a haven for bird species, reptiles, and marine life, showcasing a diverse array of wildlife that thrives in its parks and coastal waters.

In summary, Sydney's geography is a captivating blend of natural beauty and ecological richness, shaped by millennia of environmental change and human development. This dynamic landscape continues to play a crucial role in the city's identity and lifestyle.