The Great Northern Plain extends from the Punjab Plain in the west to the Brahmaputra valley in the east. The Northern Plain has been formed by the interplay of the three major river systems namely - the Indus, the Ganga and the Brahmaputra along with their tributaries. The deposition of alluvium in a vast basin lying at the foothills to the south of the Himalayas over millions of years formed this fertile plain. It spreads over an area of 7 lakh square km. The plain is about 2400 km long and 240 - 320 km broad. The rich soil cover combined with the abundant water supply and favourable climate made this agriculturally a very productive part of India. Because of this factor the density of population is also the highest in this region among all the physiographic divisions of India. The Northern Plain is broadly divided into three sections:
(a) The Punjab Plain - It is the western part of the Northern Plain formed by the Indus and its tributaries. This section is dominated by the Doabs.
(b) The Ganga Plain - It is the largest part of the Northern Plain and extends between Ghaggar and Teesta rivers.
(c) The Brahmaputra Plain - It forms the eastern part of the Northern Plain by the river Brahmaputra and its tributaries. It is narrower than the Ganga Plain and is a flood prone area.
In the south-east side of the Northern Plain lays the Ganga-Brahmaputra delta which is the largest delta of the world.