The Maldives is a long and narrow country formed by 20 natural atolls. Some atolls are made up of a number of islands, while others are isolated reefs that could be classified as smaller atoll formations. All land above the surface in the Maldives is of coralline origin.
The atolls form a fairly regular chain and, especially in the northern and central atolls, an arrayed structure is apparent, with broad and deep channels running between them. The word atoll itself comes from the Dhivehi language of the Maldives.