Atoll remains of an ancient atoll as a hill in a limestone area is called a reef knoll. The second largest atoll by dry land area is Aldabra with 155 km². The largest atoll in terms of island numbers is Huvadhu Atoll in the south of the Maldives with 255 islands. In 1842, Charles Darwin explained the creation of coral atolls in the southern Pacific Ocean based upon observations made during a five-year voyage aboard from 1831 to 1836. Accepted as basically correct, his explanation involved considering that several tropical island types—from high volcanic island, through barrier reef island, to atoll—represented
Raa Atoll the geographical and cultural point of view. However, they have become popular among tourists and foreigners in the Maldives who find them easier to pronounce than the true atoll names in Dhivehi, (save a few exceptions, like Ari Atoll)." Alifushi, located at the northern end of the atoll, is an island which has been traditionally famous for its skilled boatbuilding carpenters. It now houses shipyards. Hanikandu is the channel between Northern Maalhosmadulu Atoll and "Fasdhūtere" Atoll, beyond its southern border. This channel is also known as Moresby Channel in the honor of Robert Moresby, an almost forgotten captain and draughtsman,