The Great Plain of North India is located to the south of the Himalayas and to the north of the peninsula. It's an aggradational plain formed by three major river systems: the Indus, Ganga, and Brahmaputra. The Indo-Gangetic-Brahmaputra Plain is another name for this arcuate plain. This is the world's biggest alluvial tract, stretching 3200 kilometres from the mouth of the Indus to the mouth of the Ganga, with the Indian section alone covering 2400 kilometres. Its average breadth fluctuates between 150 and 300 kilometres. It is widest in the west, stretching for nearly 500 kilometres. Its width narrows as it travels east. It stretches for around 280 kilometres near Allahabad and 160 kilometres near the Rajmahal Hills. It extends to about 460 kilometres in West Bengal, but narrows to 60-100 kilometres in Assam. It has a total area of 7.8 million square kilometres. The Shiwalik foothills define the plain's northern limit, but its southern boundary is a wavy irregular line that runs along the northern edge of Peninsular India.

Rivers running across this plain, particularly those coming from the Himalayas, have deposited a thick layer of alluvium across its length and breadth. As a result, it is a classic aggradational plain. The thickness of the alluvium deposit, on the other hand, varies from place to place, and several estimations have been given. According to Oldham, the alluvium's maximum depth is around 5000 m on its southern boundary. It is most likely deepest between Delhi and the Rajmahal Hills, and shallowest in Rajasthan and Assam. According to latest seismic soundings calculations, the maximum depth of alluvium up to basement rocks is around 6100 metres. Meerut (1066.8 m), Kalyan (2286.0 m), and Siliguri are some of the most notable areas for alluvial deposits (5577.8 m). The morphological processes play a big role in the alluvium thickness variation. The Kosi cones in the north and Son cones in the south feature thicker alluvial deposits, whereas the intra-cone sections have shallower deposits.

The monotonous plain's main feature is its extreme horizontality. Between Ambala and Saharanpur, it reaches a maximum elevation of 291 metres above mean sea level, with an average elevation of 200 metres. The watershed that separates the Ganga and Indus drainage systems is formed by the relatively higher area around Ambala. As one enters the Punjab-Haryana plain from the Uttar Pradesh lowlands, it is in fact a low area that is barely discernible. From Saharanpur to Kolkata, the average gradient is 20 cm per km, and from Varanasi to the Ganga delta, it drops to 15 cm per km.