India’s population density is high because most of the areas have natural resources that support agriculture and industries.
Other factors like water availability and numerous cities have also caused growth of population. Population in India is unevenly distributed. The northern plains have been densely populated since centuries due to fertile land, availability of water and economic activities. Rivers like Ganga, Yamuna provide large tracts of fertile land apart from water. Also, the terrain is not a difficult one to travel. Due to availability of even fertile land and water, they prefer settling in the northern plains as opposed to the desert areas of northwest India.