A humid, low-lying, alluvial region, Bangladesh is composed mainly of the great combined delta of the Ganges, Brahmaputra, and Meghna rivers. Except for the Chittagong Hills along the Myanmar border, most of the country is no more than 300 ft (90 m) above sea level. Bangladesh is laced with numerous streams, distributaries, and tidal creeks, forming an intricate network of waterways that constitutes the country's chief transportation system. Along the southwestern coast is the Sundarbans, a mangrove swamp area with numerous low islands.
Bangladesh has a tropical monsoon climate with a distinct dry season in the winter. It receives an average annual rainfall of 80 in. (203 cm), with most falling during the summer monsoon period; the Sylhet district in the northeast is the wettest part of the country, having an annual average rainfall of 140 in. (356 cm). The low-lying delta region is subject to severe flooding from monsoon rains, cyclones (hurricanes), and storm surges that bring major crop damage and high loss of life. The cyclones of 1970 and 1991 and the monsoon floods of 1988, 1998, and 2004 were particularly devastating.
Bangladesh is one of the world's ten most populated countries and has one of the highest population densities (about 2,100 people per sq mi/810 people per sq km). The great majority of Bangladesh's population is Bengali, although Biharis and several tribal groups constitute significant minority communities. About 83% of the population is Sunni Muslim and 16% is Hindu. Bangla (Bengali) is the nation's official language, and English is used in urban centers. Bangladesh has a predominantly rural population, with over 65% of the workforce engaged in agriculture. There are several universities, including ones at Chittagong, Dhaka, Mymensingh, and Rajshahi.