Cambodia has an area of 181,035 square kilometres (69,898 square miles) and lies entirely within the tropics, between latitudes 10° and 15°N, and longitudes 102° and 108°E. It borders Thailand to the north and west, Laos to the northeast, and Vietnam to the east and southeast. It has a 443-kilometre (275-mile) coastline along the Gulf of Thailand.
Cambodia's landscape is characterized by a low-lying central plain that is surrounded by uplands and low mountains and includes the Tonle Sap (Great Lake) and the upper reaches of the Mekong River delta. Extending outward from this central region are transitional plains, thinly forested and rising to elevations of about 650 feet (200 metres) above sea level.
To the north the Cambodian plain abuts a sandstone escarpment, which forms a southward-facing cliff stretching more than 200 miles (320 kilometres) from west to east and rising abruptly above the plain to heights of 600 to 1,800 feet (180–550 metres). This cliff marks the southern limit of the Dângrêk Mountains.
Flowing south through the country's eastern regions is the Mekong River. East of the Mekong the transitional plains gradually merge with the eastern highlands, a region of forested mountains and high plateaus that extend into Laos and Vietnam. In southwestern Cambodia two distinct upland blocks, the Krâvanh Mountains and the Dâmrei Mountains, form another highland region that covers much of the land area between the Tonle Sap and the Gulf of Thailand.
In this remote and largely uninhabited area, Phnom Aural, Cambodia's highest peak rises to an elevation of 5,949 feet (1,813 metres). The southern coastal region adjoining the Gulf of Thailand is a narrow lowland strip, heavily wooded and sparsely populated, which is isolated from the central plain by the southwestern highlands.
The most distinctive geographical feature is the inundations of the Tonle Sap (Great Lake), measuring about 2,590 square kilometres (1,000 square miles) during the dry season and expanding to about 24,605 square kilometres (9,500 square miles) during the rainy season. This densely populated plain, which is devoted to wet rice cultivation, is the heartland of Cambodia. Much of this area has been designated as a biosphere reserve.