Sydney’s geographical and geological characteristics make it one of the most distinctive cities in Australia. Located on a submergent coastline, Sydney is home to a variety of natural landscapes, including deep rias, which are coastal valleys formed by rising ocean levels. The city lies within a coastal basin bordered by 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.

The city spans two major geographic regions: the relatively flat Cumberland Plain to the south and west, and the rugged Hornsby Plateau to the north, which is marked by steep valleys. These geographic features significantly influenced Sydney’s early urban development. The flat terrain of the south was the first to be developed, and it wasn’t until the completion of the Sydney Harbour Bridge that northern areas became more densely populated. Sydney’s coastline is home to 70 surf beaches, with Bondi Beach being the most famous. The Nepean River runs along the city’s western edge and transforms into the Hawkesbury River before reaching Broken Bay. Sydney’s primary water storage facilities are located along tributaries of the Nepean River, while the Parramatta, Georges, and Cooks Rivers drain the western and southern suburbs into Port Jackson and Botany Bay.

Geologically, Sydney is primarily composed of Triassic sandstone, which is found in nearly all exposed rocks around the city. The Sydney Basin, formed during the early Triassic period, features a combination of ancient sandstone, shale lenses, and fossil riverbeds. The sandstone that forms much of Sydney's landscape was deposited between 360 and 200 million years ago. Rising sea levels between 18,000 and 6,000 years ago flooded these rias, resulting in estuaries and harbours, including the world-renowned Sydney Harbour (Port Jackson). The city’s soils mainly consist of sandy soils from the Hawkesbury sandstone and clay from shale and volcanic rocks. The Wianamatta shale, found in the western part of Sydney, is a significant geological feature that contributes to the region's rich soil composition.

Sydney’s diverse geography and geology have not only shaped its natural beauty but have also played a key role in the city's historical growth and urbanization. From the fertile plains that supported early settlement to the dramatic cliffs and beaches that define its coastline, Sydney’s landscape continues to be a defining characteristic of this vibrant city.