A Brief History of Null Island
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Null Island is a fictional island in the Gulf of Guinea added to the Natural Earth public domain map dataset,[1] located where the equator crosses the prime meridian, at coordinates 0°N 0°E.[2][3] Natural Earth describes the entity as a "1 meter square island" with "scale rank 100, indicating it should never be shown in mapping."[1] Although intended humorously, the fiction has a serious purpose and is used by mapping systems to trap errors.
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(Wikipedia.)
Being centered at 0,0 (zero latitude, zero longitude) it is useful for flagging geocode failures which are routed to 0,0 by most mapping services.