SB 5.16.6
yasmin nava varsani nava-yojana-sahasrayamany astabhir maryada-giribhih suvibhaktani bhavanti.
Translation by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada:
In Jambudvipa there are nine divisions of land, each with a length of 9,000 yojanas [72,000 miles]. There are eight mountains that mark the boundaries of these divisions and separate them nicely.
Purport by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada:
Srila Visvanatha Cakravarti Thakura gives the following quotation from the Vayu Purana, wherein the locations of the various mountains, beginning with the Himalayas, are described.
dhanurvat samsthite jñeye dve varse daksinottare; dirghani tatra catvari caturasram ilavrtam iti daksinottare bharatottara-kuru-varse catvari kimpurusa-harivarsa-ramyaka-hiranmayani varsani nila-nisadhayos tirascinibhuya samudra-pravistayoh samlagnatvam angikrtya bhadrasva-ketumalayor api dhanur-akrtitvam; atas tayor dairghyata eva madhye sankucitatvena nava-sahasrayamatvam; ilavrtasya tu meroh sakasat catur-diksu nava-sahasrayamatvam sambhavet vastutas tv ilavrta-bhadrasva-ketumalanam catus-trimsat-sahasrayamatvam jñeyam.