It is a little awkward to use the name India for the entire territory of three independent states. But India in the larger sense, comprising Pakistan, India and Bangladesh together, is still a valid geographical expression. The region containing the three countries is separated from the land-mass of the rest of Asia by the highest mountain ranges in the world. From the Himalayas, lower ranges run down, on both flanks, west and east, in practically uninterrupted series, down to the sea. The sub-continent enclosed by these ranges and the sea, approximately between latitudes 8° N and 37° N and longitudes 61° E and 97° 30′ E, contains two broad physical divisions, the Indo-Gangetic plains and the peninsula.

The Indo-Gangetic plains are formed by a broad belt of alluvium of varying width, swinging from west to east in the shape of a rough crescent. The plains are themselves divisible into two great sections dominated respectively by the two river systems of the Indus and its tributaries and the Ganga and Brahmaputra and their tributaries. With the exceptions of a few rivers like the Chambal and the Son, the sources of the major rivers flowing in the plains lie in the Himalayas. In this zone, the eastern portion is the area of heavy rainfall, and as one goes west, the rivers become increasingly the major source of irrigation. Where they fail, the land becomes absolutely arid as in the Thar, the desert of Sind and western Rajasthan.