The Greenwich Meridian and why it was chosen
Geography · Key Stage 2 · The School
Longitude needs a starting line
Longitude measures distance east or west. But east or west of WHAT? Every measurement needs a starting point. That starting line is called the PRIME MERIDIAN, set at zero degrees. Without it, longitude would be meaningless.
Why Greenwich, of all places
In 1884 countries met to agree on one single line. Britain's Royal Observatory in Greenwich already led the world in mapmaking and navigation at the time. Many ships already used its charts. Greenwich won the vote, and the line has stayed there ever since. The vote was close, but Greenwich's lead was hard to argue against.
Standing on the line itself
At Greenwich, a metal strip marks the exact meridian on the ground. Stand with one foot either side and you are standing in the Eastern and Western Hemispheres at once. Every place on Earth is measured east or west from that single line. Thousands of visitors do exactly this every year. It remains one of the most visited spots in London.
Cairo sits about 31 degrees EAST of Greenwich. New York sits about 74 degrees WEST of Greenwich. Both distances are measured from the very same starting line. Without that shared agreement, every country might use its own zero point. Maps and directions would not match between countries. A single, agreed meridian is what lets every map in the world use the same numbers. A pilot flying between the two cities relies on that agreement every single flight.