The narrow lowland strips that fringe the Peninsular plateau on the west and east, lying between the Ghats and the sea, divided into the Western and Eastern Coastal Plains.
- The Western Coastal Plain runs from Gujarat to Kerala between the Western Ghats and the Arabian Sea; it is narrow, with sub-parts named the Konkan (Maharashtra-Goa), Kanara (Karnataka), and Malabar (Kerala) coasts.
- The Western Coast is a submerged coast with little delta formation but good natural harbours (such as Mumbai, Marmagao, Kochi); the rivers form estuaries, and Kerala has lagoons and backwaters called kayals.
- The Eastern Coastal Plain runs from West Bengal to Tamil Nadu between the Eastern Ghats and the Bay of Bengal; it is broader and is named the Northern Circars (north) and the Coromandel Coast (south, Tamil Nadu).
- The Eastern Coast is an emergent coast with wide, fertile deltas built by the Mahanadi, Godavari, Krishna, and Kaveri; it has fewer good natural harbours, so many are artificial (for example Chennai).
- The Chilika Lake (Odisha) and the Pulicat Lagoon (Andhra-Tamil Nadu border) are notable lagoons on the eastern coast; Chilika is India's largest brackish-water lagoon.
The west-versus-east contrast (narrow submerged with harbours and estuaries against broad emergent with deltas), the named coastal sub-divisions, and the major lagoons are recurring physiography facts and matching items. The long coastline is also central to coastal security.
The Western Coast is narrow, submerged, harbour-rich, with estuaries; the Eastern Coast is broad, emergent, delta-rich, with fewer natural harbours. Konkan-Kanara-Malabar are western sub-parts; Northern Circars and Coromandel are eastern.
Two coastal lowlands: narrow submerged Western Coast (harbours, estuaries, backwaters) and broad emergent Eastern Coast (deltas, lagoons).