Vietnam is located on the eastern Indochinese Peninsula between the latitudes 8° and 24°N, and the longitudes 102° and 110°E. It covers a total area of approximately . The combined length of the country's land boundaries is , and its coastline is  long. At its narrowest point in the central Quảng Bình Province, the country is as little as  across, though it widens to around  in the north. Vietnam's land is mostly hilly and densely forested, with level land covering no more than 20%. Mountains account for 40% of the country's land area, and tropical forests cover around 42%. The Red River Delta in the north, a flat, roughly triangular region covering , is smaller but more intensely developed and more densely populated than the Mekong River Delta in the south. Once an inlet of the Gulf of Tonkin, it has been filled in over the millennia by riverine alluvial deposits. The delta, covering about , is a low-level plain no more than  above sea level at any point. It is criss-crossed by a maze of rivers and canals, which carry so much sediment that the delta advances  into the sea every year. The exclusive economic zone of Vietnam covers  in the South China Sea.