South Asia is home to about two billion people, roughly one-fourth of the world's population. India has by far the largest population in the region, while Pakistan and Bangladesh also contain very large populations. Nepal, Sri Lanka, Bhutan, and Maldives have much smaller total populations, but population density varies greatly within every country.
Some of the densest settlement is found across the broad plains of northern India, eastern Pakistan, and Bangladesh. These areas contain major river systems, relatively flat land, fertile soils, transportation routes, farms, towns, and large cities. Bangladesh is especially densely populated, with many people living on the lowlands formed by the Ganges, Brahmaputra, and other rivers.
Pakistan also shows a strong connection between population and the Indus River system. Much of the country's population is concentrated near the Indus and its tributaries, where water supports farming and cities. In India, dense settlement stretches across much of the Ganges Plain and around major metropolitan areas such as Delhi and Kolkata.
Mountainous areas generally have lower population densities. Steep slopes, high elevation, colder temperatures, and difficult transportation can limit the amount of land available for large settlements or farming. In Nepal, for example, settlement is much denser in valleys and lower areas than in the highest Himalayas. Bhutan also has large mountainous areas with relatively low population density.
Physical geography is important, but it is not the only reason people live where they do. Cities grow because they provide jobs, transportation, education, government services, trade, and other opportunities. Historical settlement patterns also matter. Population distribution therefore reflects the interaction of physical geography with human decisions made over many generations.