Prime Meridian Map
The prime meridian (0° longitude) is the reference line for every map and every clock on Earth. Trace it from Greenwich through France, Spain and Africa, and learn how an 1884 vote in Washington made one London observatory the zero point of world navigation.
The 8 countries on the prime meridian
North to south:
- 1United Kingdom — The line's home: it passes through the Royal Observatory at Greenwich, London, where the Airy Transit Circle defines 0°.
- 2France — Crosses eastern France — Paris once championed its own Paris meridian as the world standard.
- 3Spain — Passes just west of Valencia, through the town of Castellón de la Plana's region.
- 4Algeria — Enters Africa through the northern coastal mountains and the Sahara beyond.
- 5Mali — Through the Saharan north of the country, near the historic trading region.
- 6Burkina Faso — A short crossing in the country's north.
- 7Togo — Clips the western edge of the country.
- 8Ghana — Exits Africa at Tema, just east of Accra — Ghana's name echoes the region's history, not the meridian.
How Greenwich became zero
Before 1884, every maritime nation kept its own zero meridian — Paris, Cádiz, Naples, Washington and others all had supporters. The International Meridian Conference in Washington, D.C., with delegates from 25 nations, settled it: the meridian through the Royal Observatory at Greenwich, London, would be the world's prime meridian, and the universal day would begin at midnight there. Greenwich won largely because most of the world's shipping already navigated by British charts.
The brass line tourists straddle in Greenwich park marks the Airy Transit Circle, the telescope that defined 0° for over a century. Modern geodesy has moved on slightly: the IERS Reference Meridian used by GPS runs about 102 metres east of the historic brass line, because it is computed from the planet's mass centre rather than a single observatory. For everyday navigation the difference is invisible.
The prime meridian is the anchor of the entire longitude system — and of world time. Greenwich Mean Time grew directly out of it, and today's Coordinated Universal Time (UTC) is its atomic-clock successor. Every time zone on Earth is still defined as an offset from the line on this map.
How to use this tool
Follow the amber line from the Arctic Ocean through Europe and Africa to Antarctica; the Greenwich marker is pinned.
Eight crossings are listed north to south, from the UK to Ghana.
Why 25 nations voted Greenwich zero, and how GMT became UTC.
What people use this tool for
Every UTC offset on Earth is defined east or west of this line.
Why charts, GPS and aviation all anchor longitude here.
What the brass line, the Airy Transit Circle and the 102-metre offset mean for visitors.
How it's calculated
The modern prime meridian is the IERS Reference Meridian, computed from the Earth's mass centre; it runs about 102 metres east of the historic Airy Transit Circle brass line at Greenwich. Country crossings follow current international boundaries from the North Pole to the South Pole.
Related tools and resources
Frequently asked questions
What is the prime meridian?
The 0° longitude line — the reference meridian from which all other longitudes are measured east and west.
Which countries does the prime meridian pass through?
Eight: the United Kingdom, France, Spain, Algeria, Mali, Burkina Faso, Togo and Ghana.
Why Greenwich?
At the 1884 International Meridian Conference in Washington, 25 nations voted for Greenwich — largely because most of the world's shipping already navigated by British charts.
What is the difference between GMT and UTC?
GMT is the historic mean solar time at Greenwich; UTC is its modern atomic-clock successor, kept within 0.9 seconds of Earth's rotation.
Is the GPS zero line exactly at Greenwich?
Almost — the IERS Reference Meridian used by GPS runs about 102 metres east of the historic brass line in Greenwich park.
What is the opposite of the prime meridian?
The 180° meridian — the basis of the International Date Line, where each new calendar day begins.