Centuries ago, when maps were first drawn, there were no satellites or Google Maps. People had no choice but to rely on the tales of explorers, when drawing maps.
As a result these maps were often not accurate, and many of them contained islands known as phantom islands. Phantom Islands are islands that were believed to have existed.
They would have appeared on maps for a period of time- sometimes for centuries. However, once it was proved that they did not exist, these islands have been removed from world maps. Phantom Islands might have been a misrepresentation of actual islands.