Matsya Purana — Division of Bhārata-varṣa
तस्य नाम्ना समाख्यातो जम्बूद्वीपो वनस्पतेः योजनानां सहस्रं च शतधा च महान्पुनः //
tasya nāmnā samākhyāto jambūdvīpo vanaspateḥ yojanānāṃ sahasraṃ ca śatadhā ca mahānpunaḥ //
This continent is called Jambūdvīpa after that Jambū tree; moreover, it is vast, extending to one hundred thousand yojanas.
This verse is not about Pralaya; it belongs to cosmography, explaining how Jambūdvīpa is named after the Jambū tree and giving its traditional Puranic measurement (100,000 yojanas).
Indirectly, it supports the king’s and householder’s dharma by grounding pilgrimage, sacred geography, and the cosmic order (loka-vyavasthā) that rulers are expected to protect; it is primarily descriptive rather than prescriptive.
No direct Vāstu or ritual rule is stated; however, knowing Jambūdvīpa’s sacred-geographical framework is used in Purāṇic ritual imagination (mandala-style world-maps, tīrtha orientation, and cosmological visualization in worship).