Onotoa is an atoll

Atoll

An atoll is a coral island that encircles a lagoon partially or completely.- Usage :The word atoll comes from the Dhivehi word atholhu OED...

 and district

District

Districts are a type of administrative division, in some countries managed by a local government. They vary greatly in size, spanning entire regions or counties, several municipalities, or subdivisions of municipalities.-Austria:...

 of Kiribati

Kiribati

Kiribati , officially the Republic of Kiribati, is an island nation located in the central tropical Pacific Ocean. The permanent population exceeds just over 100,000 , and is composed of 32 atolls and one raised coral island, dispersed over 3.5 million square kilometres, straddling the...

. It is situated in the Gilbert Islands

Gilbert Islands

The Gilbert Islands are a chain of sixteen atolls and coral islands in the Pacific Ocean. They are the main part of Republic of Kiribati and include Tarawa, the site of the country's capital and residence of almost half of the population.-Geography:The atolls and islands of the Gilbert Islands...

 in the Pacific Ocean

Pacific Ocean

The Pacific Ocean is the largest of the Earth's oceanic divisions. It extends from the Arctic in the north to the Southern Ocean in the south, bounded by Asia and Australia in the west, and the Americas in the east.At 165.2 million square kilometres in area, this largest division of the World...

, 65 km from Tamana, the smallest island in the Gilberts.

The atoll is similar to many other atolls in the Gilbert Islands with its continuous line of islet

Islet

An islet is a very small island.- Types :As suggested by its origin as islette, an Old French diminutive of "isle", use of the term implies small size, but little attention is given to drawing an upper limit on its applicability....

s and island

Island

An island or isle is any piece of sub-continental land that is surrounded by water. Very small islands such as emergent land features on atolls can be called islets, cays or keys. An island in a river or lake may be called an eyot , or holm...

s on the eastern side. The western side consists of a submerged reef

Reef

In nautical terminology, a reef is a rock, sandbar, or other feature lying beneath the surface of the water ....

 which surrounds the islet filled lagoon

Lagoon

A lagoon is a body of shallow sea water or brackish water separated from the sea by some form of barrier. The EU's habitat directive defines lagoons as "expanses of shallow coastal salt water, of varying salinity or water volume, wholly or partially separated from the sea by sand banks or shingle,...

.