Seen from the air, the Bahamas is a swirling mass of deep blue ocean, dotted with patches of turquoise water and a strip of islands rimmed in white sand. These 700 low-lying islands, along with over 2,400 islets called cays, are surface projections of two oceanic banks composed of coral with a limestone base. Around the islands is found approximately 5% of the world's coral, an amount surpassing even Australia's Great Barrier Reef. Extending from 80km (50mi) east of Florida to 80km (50mi) northeast of Cuba and crossing the Tropic of Cancer, technically speaking, the archipelago is not a part of the Caribbean. All the eastern 'out islands' have good surfing potential but only Abaco and Eleuthera receive traveling surfers on a regular basis. During the '70s, Puerto Rican surfers expanded their horizons and the Bahamas became a hot surfing destination but during the '80s its popularity began to fade as places such as Costa Rica became known for being cheaper and more consistent.