It is due to:
1.alluvial soil
2.natural vegetation
5.comfortable life
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Indo gangetic plains have high density of population due to the following reasons:
1.alluvial soil:the alluvial soil is very fertile and supports cultivation of different types of crops.
2.natural vegetation:tropical deciduous forests dominate the region which provides timber, fuel wood, medicinal plants etc,.
3.topography: the land area has varied topography. the mountain areas with steep slopes have scarce population but the plain areas provide the most suitable land for human habitation.
4.transport:transport is well developed in the indo gangetic plains. in the plain areas the road ways and railways are modes of cheap transport.

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