Where is the prime meridian?

At the International Meridian Conference in Washington in 1884, delegates from 25 nations chose the Greenwich meridian as the world’s starting line for longitude. It was picked largely because most of the world’s shipping charts already used it. The line runs from the North Pole through the UK, France, Spain, Algeria, Mali, Burkina Faso, Togo and Ghana before crossing Antarctica to the South Pole. Greenwich Mean Time, based on this line, became the reference for world time zones. Visitors to the Royal Observatory can stand with one foot in each hemisphere.