The name for a cluster or chain of islands is "archipelago".
(More technically, it would apply to a chain of islands like Hawaii, which are all formed from the same tectonic / volcanic source.)
an archipelago
Geographers call an island chain an Archipelago.
archipelago
Oceania.
An archipelago
It is called an archipelago.
metropolitan areas
eqyator
Prime Meridian
They call it physical features.
Greenwich mean time [gmt]
the prime meridian