Vietnam is located on the eastern margin of the Indochinese peninsula and occupies about 331,688 square kilometers, of which about 25 % was under cultivation in 1987. It borders the Gulf of Thailand, Gulf of Tonkin, and South China Sea, alongside China, Laos, and Cambodia. The S-shaped country has a north-to-south distance of 1,650 kilometers and is about 50 kilometers wide at the narrowest point. With a coastline of 3,260 kilometers, excluding islands, Vietnam claims 12 nautical miles (22.2 km; 13.8 mi) as the limit of its territorial waters, an additional 12 nautical miles (22.2 km; 13.8 mi) as a contiguous customs and security zone, and 200 nautical miles (370.4 km; 230.2 mi) as an exclusive economic zone.
The boundary with Laos, settled, on an ethnic basis, between the rulers of Vietnam and Laos in the mid-seventeenth century, was formally defined by a delimitation treaty signed in 1977 and retified in 1986. The frontier with Cambodia, defined at the time of French annexation of the western part of the Mekong River 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 that China agreed in 1957- 58 to respect. However, in February 1979, following China's limited invasion of Vietnam, 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.
Vietnam is a country of tropical lowlands, hills, and densely forested highlands, with level land covering no more than 20% of the area. The country is divided into the highlands and the Red River delta in the north; and the Giai Truong Son (Central mountains, or the Chaîne Annamitique, sometimes referred to simply as "the Chaine."), the coastal lowlands, and the Mekong River Delta in the south.
The spectacular Ban Gioc Waterfall is 272 km north of Hanoi and few tourists are seen there.
The delta of the Red River (also known as the Sông Hồng), is a flat, triangular region of 15,000 square kilometers[2], is smaller but more intensely developed and more densely populated than the Mekong River Delta. Once an inlet of the Gulf of Tonkin, it has been filled in by the enormous alluvial deposits of the rivers over a period of millennia, and it advances one hundred meters into the Gulf annually. The ancestral home of the ethnic Vietnamese, the delta accounted for almost 70 % of the agriculture and 80 % of the industry of North Vietnam before 1975.
The Red River, rising in China's Yunnan province, is about 1,200 kilometers long. Its two main tributaries, the Sông Lô (also called the Lo River, the Riviere Claire, or the Clear River) and the Sông Da (also called the Black River or Riviere Noire), contribute to its high water volume, which averages 4,300 cubic meters per second.[3] The entire delta region, backed by the steep rises of the forested highlands, is no more than three meters above sea level, and much of it is one meter or less. The area is subject to frequent flooding; at some places the high-water mark of floods is fourteen meters above the surrounding countryside. For centuries flood control has been an integral part of the delta's culture and economy. An extensive system of dikes and canals has been built to contain the Red River and to irrigate the rich rice-growing delta. Modeled on that of China's, this ancient system has sustained a highly concentrated population and has made double-cropping wet-rice cultivation possible throughout about half the region.
Vietnam has a tropical monsoon climate, with humidity averaging 84 % throughout the year. However, because of differences in latitude and the marked variety of topographical relief, the climate tends to vary considerably from place to place. During the winter or dry season, extending roughly from November to April, the monsoon winds usually blow from the northeast along the China coast and across the Gulf of Tonkin, picking up considerable moisture; consequently the winter season in most parts of the country is dry only by comparison with the rainy or summer season. During the southwesterly summer monsoon, occurring from May to October, the heated air of the Gobi Desert rises, far to the north, inducing moist air to flow inland from the sea and deposit heavy rainfall.
Annual rainfall is substantial in all regions and torrential in some, ranging from 1,200 to 3,000 millimeters (47.2 to 118.1 in). Nearly 90 % of the precipitation occurs during the summer. The average annual temperature is generally higher in the plains than in the mountains and plateaus. Temperatures range from a low of 5 °C (41 °F) in December and January, the coolest months, to more than 37 °C (98.6 °F) in April, the hottest month. Seasonal divisions are more clearly marked in the northern half than in the southern half of the country, where, except in some of the highlands, seasonal temperatures vary only a few degrees, usually in the 21–28 °C (69.8–82.4 °F) range
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