The geographical concepts of Hindu Puranas developed from their nucleus in the Vedic literature, as typified in Nadi Sukta of Rig Veda and Prithvi Sukta of Atharva Veda. Traces of regions geography of India are first found in Aitareya Brahmana.
Climatology, meteorology and geography have been treated in detail in Bhuvanakosha sections of Puranas. The term Bhuvanakosha is technical in its meaning and corresponds to the modern term ‘geography.’ In almost all Puranas, some ten to fifteen chapters are devoted to the description of geography. They are conventionally arranged and are reasonably authentic, except occasionally when mythology interferes with scientific treatment of the subject. Puranas like Vayu, Matsya and Brahmanda elaborately describe the climatic and weather phenomena. Puranic geography also includes astronomy in its scope. Similarly, Siddhanta works include jyotisha in the domain of geography. The term bhugola (round or oval earth) is first used in Surya Siddhanta, Bhugoladhyaya.
Puranic ideas of cosmography and geography begin with the concept of the world consisting of seven concentric islands (Sapta Dvipa Vasumati), each one of which is encircled by a sea. The central island is known as Jambudvipa, which extends over the north-west, the north and the south of the Himalayas, i.e., Eurasia of the modern terminology. One of its subdivisions is conceived as the land bounded by the Himalayas in the north and Indian Ocean in the west, south and the east. It is further divided into five directional portions of Uttarapatha, Madhyadesha, Dakshinapatha, Praci and Pratici, and its smaller divisions are conceived as consisting of a large number of janapadas (regions) inhabited by peoples of distinctive habits, customs and manners.
By the time Puranas were composed, the knowledge and number of the janapadas, their peoples, places of pilgrimage (tirthas), rivers and mountains had grown in varied dimensions. The pancajanah (five tribes) of Rig Veda situated in Punjab grew to a conventional number of sixteen mahajanapadas in the time of Vardhamana Mahavira and Buddha, as is evident from Anguttara Nikaya.
By the early medieval period, Puranas had begun to conceive India as a land of 56 regions. Sapta or seven became a conventional number to denote cultural and religious importance of cities, rivers and mountains. There were seven moksha dayika (liberating) cities – Ayodhya, Maya, Mathura, Kashi, Kanchi, Avantika and Dvaravati: seven purest of the pure rivers – Ganga, Yamuna, Godavari, Saraswati, Narmada, Sindhu and Kaveri; and seven kula parvatas – Mahendra, Malaya, Sahya, Sutimana, Riksha, Vindhya and Pariyatra. The numerical concept of seven had already been present in the seven rivers of the Vedic systems (sapta sindhu) and the seven mouths (saptamukhas) of the Sindhu and Ganga rivers. Puranas further developed this concept in describing the earth as consisting of Sapta Dvipa Vasumati (seven islands) and Saptarishi (seven stars) in the sky. A detailed list of religious and sectarian centers of India with descriptions of the Kashi Khanda, the Avanti Khanda, and the Kedara Khanda is given in the Skanda Purana.
Cambridge History of India Vol I (1922) Edited by A B Keith published by Cambridge University Press
Encyclopedia of Hinduism – IHRF – Volume IV page 276