Located in the centre of the Indochina peninsula, without direct access to the sea, the Lao People´s Democratic Republic covers a surface area of approximately 236 800 km2. It is bounded on the north by China and Vietnam, on the east by Vietnam, on the south by Cambodia, on the west by Thailand and on the north-west by Myanmar. Its long border with Thailand is largely formed by the course of Mekong River and the border with Viet Nam generally skirts the Annamite Range.
Excluding the alluvial plains of the valley of the Mekong and lower courses of its tributaries below 200 meters, the remainder of country (approximately 80 percent) is mountainous, and a little more half ranges between 1 000 and 2 000 m elevation.
Large, flat alluvial valleys extend along the rivers draining to the Mekong from the plain. Rugged plateaus lie between them with the larger mountains having elevations of 200 to 500 m. The Annamite Mountains spread to the south, paralleling the border of Vietnam and sometimes exceeding 2 500 m. They end in the southern extreme of the country in plateaus of 1 000 to 2 000 m elevation.
The whole country is drained to the east by Mekong (and its principal rivers such as the Nam Ngum), running toward Cambodia. The exception is the eastern area of northern Laos, the plateau of Nongkang in particular, that drains toward the gulf of Tonkin.
The topography creates quite distinct climates. The low areas are wet tropical while the higher areas above 1 000 meters have humid subtropical or humid montane climates. The area of the two climatic types is about equal in Laos. In the low areas, the average annual temperature ranges from 24° to 27° C. In the higher areas, the averages are appreciably less: 20° C and lower.
This distinction is not as clear with regard to precipitation. Often, there is plentiful rainfall at low altitude in proximity to the mountains (Boneng has 3 750 mm at 180 meters of altitude) and, conversely, there are mountainous areas with less precipitation (Sam Neua has 1 460 mm at 940 m of altitude). The dry season varies according to the area and its duration varies between 2 and 5 months (2 to 3 months in the area of Paksane, 4 to 5 months in the valley of the Mekong). The monsoon season generally lasts from May to September.
The designations employed and the presentation of material in this publication do not imply the expression of any opinion whatsoever on the part of the Food and Agriculture Organization of the United Nations concerning the legal status of any country, territory, city or area or of its authorities, or concerning the delimitation of its frontiers or boundaries.