Question

Why do we find high population densities in the Northern Plains?

Answer 1

Hint:
Rugged, hilly dissected and rocky nature of the terrain, shallow and less fertile soil, and unfavourable climatic conditions like moderate to low rainfall. They are primarily responsible for the sparse population anywhere.

Complete answer:
Just like rugged terrains and uneven landforms are sparsely populated. Life-sustaining elements are more likely to attract population, which are provided by the Northern Plains. The various reasons for which the northern plain is the densely populated area:
Fertile land: River valleys are more fertile due to alluvial deposits. Fertile lands have high agricultural productivity which is essential for human life.
Water Availability: Water is the most important factor in considering a place suitable for living. Abundant water is essential for Urbanisation and Industrialisation as well as provides irrigation to farmlands.
Uniform Landform: Flat Plain areas are not only suitable for agricultural and house construction but they are also suitable for the establishment of industries and expansion of transport. Transport systems are the nerves of the economy. Maintenance of roads and ease of construction allow dense networks.
Climate factor: Northern Plains avoid mainly two conditions which are arid and semi-arid climate of desert and Chilly and Snowy cold climate of mountain regions. They also receive abundant rainfall.
Although the climate of the Northern Plain is not as suitable or pleasant as of coastal regions, which are pleasant due to the moderating effect of the sea, it is also not very harsh.
Thus, high population densities are found in the Northern Plains.

Note:
To conduct human lives and businesses profitably we need a robust connectivity network, alluvial soil deposits, and perennial water resource base which are essential to sustain a large population.