The distribution pattern of the railway network in India has been greatly influenced by physical and economic factors. Level lands of the Northern Plains of India with high density of population, rich agricultural resources and greater industrial activity have favoured the development of railways in this region. The region, therefore, has the densest network of railways in India. The rugged terrain of the Himalayan mountain region in the north and the north-eastern states with sparse population and lack of economic opportunities are unfavourable for construction of railway lines and railway network is lacking in these regions. Sparsely populated sandy deserts of Rajasthan, hilly contiguous tracts of the Sahyadri swamps of Gujarat, forested tracks of Madhya Pradesh, Chhattisgarh, Orissa and Jharkhand, frequently flooded floodplains of Bihar and Assam have posed great difficulty in laying of railway lines. On account of the economic importance of the region, the Konkan Railways were developed in recent times along the west coast in spite of problems of sinking of tracks, landslides and need for construction of tunnels.