Maldives consists of approximately 1,200 coral islands grouped in a double chain of twenty-seven atolls. Composed of live coral reefs and sand bars, these atolls are situated atop a submarine ridge 960 kilometers long that rises abruptly from the depths of the Indian Ocean and runs from north to south. Only near the southern end of this natural coral barricade do two open passages permit safe ship navigation from one side of the Indian Ocean to the other through the territorial waters of Maldives. For administrative purposes the Maldives government organized these atolls into nineteen administrative divisions.