Burma consists primarily of a central lowland surrounded by mountains and plateaus. The lowland, which consists mainly of the Irrawaddy, Chindwin, and Sittang river valleys, extends some 700 miles (1,130 km) northward from the Irrawaddy delta. Concentrated here is most of the country's population. Enclosing the central lowland on the west and north are thickly forested mountains, which rise to more than 19,000 feet (5,800 m) in the far north. Rimming the eastern edge of the central lowland and occupying most of east-central Burma is the Shan Plateau, an undulating region that averages 3,000 feet (900 m) in elevation. Much of the plateau is drained by the Salween River, whose course is marked by numerous gorges and rapids.
Most of Burma lies within the tropics, and the low-lying areas have warm weather all year. In Mandalay, for example, average monthly temperatures vary from 68° to 89° F. (20° to 32° C.); in Rangoon, from 77° to 86° F. (25° to 30° C.). The highest temperatures occur in April, just before the summer monsoon rains begin. The rains continue through October, by which time most of the year's total rainfall has been received. Rainfall along most of the coast totals more than 200 inches (5,000 mm) a year, with amounts gradually decreasing toward the interior. In the central lowland around Mandalay and Myingyan is an area known as the Dry Belt, which receives less than 40 inches (1,000 mm) a year.