SB 5.16.6

yasmin nava varṣāṇi nava-yojana-sahasrāyāmāny aṣṭabhir maryādā-giribhiḥ suvibhaktāni bhavanti.
Word for word: 
yasmin — in that Jambūdvīpa; nava — nine; varṣāṇi — divisions of land; nava-yojana-sahasra — 72,000 miles in length; āyāmāni — measuring; aṣṭabhiḥ — by eight; maryādā — indicating the boundaries; giribhiḥ — by mountains; suvibhaktāni — nicely divided from one another; bhavanti — are.
Translation: 
In Jambūdvīpa 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: 

Śrīla Viśvanātha Cakravartī Ṭhākura gives the following quotation from the Vāyu Purāṇa, wherein the locations of the various mountains, beginning with the Himālayas, are described.

dhanurvat saṁsthite jñeye dve varṣe dakṣiṇottare; dīrghāṇi tatra catvāri caturasram ilāvṛtam iti dakṣiṇottare bhāratottara-kuru-varṣe catvāri kiṁpuruṣa-harivarṣa-ramyaka-hiraṇmayāni varṣāṇi nīla-niṣadhayos tiraścinībhūya samudra-praviṣṭayoḥ saṁlagnatvam aṅgīkṛtya bhadrāśva-ketumālayor api dhanur-ākṛtitvam; atas tayor dairghyata eva madhye saṅkucitatvena nava-sahasrāyāmatvam; ilāvṛtasya tu meroḥ sakāśāt catur-dikṣu nava-sahasrāyāmatvaṁ saṁbhavet vastutas tv ilāvṛta-bhadrāśva-ketumālānāṁ catus-triṁśat-sahasrāyāmatvaṁ jñeyam.