Vietnam is located on the eastern margin of the Indochinese peninsula and occupies about 331,211.6 square kilometers, of which about 25% was under cultivation in 1987. It borders the Gulf of Tonkin, Gulf of Thailand, and Pacific Ocean, along with China, Laos, and Cambodia. The elongated roughly S shaped country has a north-to-south distance of and is about wide at the narrowest point. With a coastline of , excluding islands, Vietnam claims as the limit of its territorial waters, an additional as a contiguous customs and security zone. It has an exclusive economic zone of with . The boundary with Laos was settled on both an ethnic and geographical basis between the rulers of Vietnam and Laos in the mid-seventeenth century. The Annamite Range as a reference, was formally defined by a delimitation treaty signed in 1977 and ratified in 1986. The frontier with Cambodia, defined at the time of French annexation of the western part of the Mekong Delta in 1867, remained essentially unchanged, according to Hanoi, until some unresolved border issues were finally settled in the 1982–85 period. The land and sea boundary with China, delineated under the France-China treaties of 1887 and 1895, is "the frontier line" accepted by Hanoi. China agreed in 1957–58 to respect that border line. However, in February 1979, following the Sino-Vietnamese War, Hanoi complained that from 1957 onward China had provoked numerous border incidents as part of its anti-Vietnam policy and expansionist designs in Southeast Asia. Among the territorial infringements cited was the Chinese occupation in January 1974 of the Paracel Islands, claimed by both countries in a dispute left unresolved in the 1980s. Physiography The country is divided into the highlands and the Hong River Delta in the north, the Annamite Range along with the coastal lowlands in the centre, and the Mekong Delta in the south. Terrain Vietnam is a country of tropical lowlands, hills, and densely forested highlands, with level land covering less than 20% of the area. The spectacular Bản Giốc Waterfall is 272 km north of Hanoi and few tourists are seen there. Red River Delta The joined Delta of Hong River (Red River) and Thái Bình River is a flat, triangular region of 15,000 square kilometers. The Hong River Delta is smaller but more intensely developed and more densely populated than the Mekong Delta. Once an inlet of the Gulf of Tonkin, it has been filled