Prime Meridian — World Map, Countries It Crosses, and Why Greenwich
The Prime Meridian is the line of 0° longitude — the universal reference for longitude on Earth. Defined in 1884 to pass through the Royal Observatory in Greenwich, it crosses 8 countries from the Arctic to the Gulf of Guinea on its 20,037 km journey from pole to pole.
| # | Country | Length crossed | Capital | Population | Climate |
|---|---|---|---|---|---|
| 1 | United KingdomRoyal Observatory Greenwich — the official home of 0° longitude | … | London | 67.5M | Oceanic temperate |
| 2 | FranceEnters near Villers-sur-Mer (Calvados); crosses central France | … | Paris | 67.8M | Oceanic / continental |
| 3 | SpainCrosses Aragón near Lleida and Castellón | … | Madrid | 47.8M | Mediterranean / continental |
| 4 | AlgeriaCrosses the northern Sahara | … | Algiers | 45.4M | Mediterranean coast / Saharan desert |
| 5 | MaliCrosses eastern Mali through the Gao region near the Niger River | … | Bamako | 22.6M | Sahel / Saharan |
| 6 | Burkina FasoCrosses the eastern Sahel near Fada N'gourma | … | Ouagadougou | 22.7M | Sahel / tropical savanna |
| 7 | TogoClips western Togo along the Ghana border in the Savanes region | … | Lomé | 8.8M | Tropical savanna |
| 8 | GhanaExits at the Atlantic coast near Tema, just east of Accra | … | Accra | 33.5M | Tropical savanna / humid coast |
Bodies of water crossed
Quick facts
- The Prime Meridian was set at Greenwich in 1884 by the International Meridian Conference — 22 of 25 countries voted in favour.
- The actual zero of GPS coordinates (the IERS Reference Meridian) sits about 102 metres east of the Greenwich Observatory line — the original measurement was made when Earth’s gravity was less precisely understood.
- The Prime Meridian is the basis for Greenwich Mean Time (GMT), now superseded by Coordinated Universal Time (UTC).
- No country other than the UK has a major capital city on the Prime Meridian — Accra (Ghana) is the closest, sitting just 1° west.
- Where the Prime Meridian crosses the Equator (0°N 0°E) is a point in the Atlantic Ocean called Null Island — about 615 km south of the Ghana coast, the closest land.
- The Prime Meridian is half of a great circle — its other half is the 180° antimeridian, the basis of the International Date Line.
What is the Prime Meridian? Definition and Geographic Facts
The Prime Meridian is the line of 0° longitude — the universal reference against which every other longitude on Earth is measured. East of the line, longitudes are positive (running up to +180° at the antimeridian); west of the line, longitudes are negative (down to -180°, the same antimeridian). Together, the Prime Meridian and the antimeridian form a single great circle that splits Earth into the Eastern and Western Hemispheres.
Prime Meridian definition (short): the line of 0° longitude, set in 1884 to pass through the Royal Observatory in Greenwich, England. Prime Meridian length:20,037 km (12,450 mi), exactly half of Earth's polar circumference. Prime Meridian latitude range: from the North Pole (90° N) to the South Pole (90° S), passing through the Equator at 0°N 0°E in the Atlantic Ocean.
Where is the Prime Meridian on a world map?On any standard world map, the Prime Meridian is the vertical line that splits the map roughly in two — running through Western Europe (the UK, France, Spain), then south through Western Africa (Algeria, Mali, Burkina Faso, Togo, Ghana), and finally through the Atlantic Ocean to Antarctica's Queen Maud Land. About 4,500 km of the Prime Meridian crosses land; the rest is ocean and Antarctic ice.
Unlike the Equator and the polar circles — which are fixed by Earth's rotation and axial tilt — the Prime Meridian is set by international agreement, not by any natural feature. Other countries historically used their own prime meridians (Paris, Cádiz, Washington, Pulkovo) until the 1884 International Meridian Conference unified the world on Greenwich. The choice was political and practical, not astronomical.
How to use this Prime Meridian map
- Open the world map. The vertical green line is the Prime Meridian — 0° longitude — running from the North Pole down to the South Pole. It is exactly 20,037 km long (half of Earth's polar circumference). The 8 countries the meridian passes through are highlighted with a translucent fill.
- Click any country to see entry/exit latitudes and length traversed. Click any highlighted country (or any row in the table below) to open a popup showing the exact latitudes where the Prime Meridian enters and exits. Together the 8 countries account for about 4,500 km of land — the rest of the meridian's length is open ocean and Antarctic ice.
- Sort the countries table by length, name, or population. The reference table lists all 8 countries with capital, population, climate, and length the meridian traverses. Click any column to sort. Algeria is the longest land stretch; the United Kingdom is where it all began at the Royal Observatory in Greenwich.
- Read the Greenwich, Null Island, and time-zone notes. Below the map: the history of why Greenwich is the world's reference (1884), the 102-metre offset between the historical Greenwich line and the modern IERS reference, why 0°N 0°E is called Null Island, and how the Prime Meridian anchors every time zone on Earth.
The 8 countries the Prime Meridian passes through
From north to south, here is what the Prime Meridian crosses in each country, with the landmarks, towns, and ecological zones along the line.
United Kingdom
The Prime Meridian was defined to pass through the Royal Observatory in Greenwich, London — the original reason for its location at 0° longitude. The line enters the UK at the Yorkshire coast near Tunstall in the East Riding, passes south through Lincolnshire (just east of Boston), through Cambridgeshire, then through London just east of the City. At Greenwich, the meridian is marked by a brass strip set into the cobblestones at the Royal Observatory courtyard — the most-photographed line in the world. It exits the UK at the south coast near Peacehaven, East Sussex.
France
Enters France at the Normandy coast near Villers-sur-Mer (Calvados), about 30 km east of Caen, where a small monument marks the crossing on the seafront. The line passes south through Pays de la Loire and Indre, near (but not through) Le Mans and Tours, then continues across the Massif Central down to the Pyrenees border with Spain. France has the second-longest Prime Meridian land stretch after Algeria.
Spain
The meridian enters Spain at the central Pyrenees and crosses the country south through Aragón and Catalonia. Major nearby cities include Lleida and Castellón de la Plana — both within 50 km of the line. The meridian exits Spain at the Mediterranean coast near El Vendrell in Catalonia, then crosses about 600 km of Mediterranean Sea (passing east of the Balearic Islands) before reaching the African coast.
Algeria
Enters Algeria at the Mediterranean coast near Mostaganem and passes about 1,700 km south through the country — by far the longest land stretch of the Prime Meridian. The line crosses the Tell Atlas mountains, then descends into the northern and central Sahara. The Algerian section is some of the most sparsely populated land on Earth, dominated by sand seas and rocky hamadas.
Mali
The meridian crosses Mali through the country's eastern Sahel region around Gao and Ansongo. The Niger River runs roughly east-west across this region and is the dominant geographic feature. Population is concentrated along the river; the rest is sparsely inhabited semi-desert giving way to true Sahel.
Burkina Faso
Crosses eastern Burkina Faso through the Est region (Province de la Gnagna and Tapoa). The closest sizeable town to the line is Fada N'gourma, about 60 km west. The W National Park — a vast UNESCO-listed savanna reserve shared with Niger and Benin — sits just east of the meridian and is a stronghold for West African elephants and lions.
Togo
The Prime Meridian clips the western edge of Togo along its border with Ghana in the Savanes region. The Togo-Ghana border runs near (and in places along) longitude 0°, so the meridian's path through Togo is brief. North of the meridian's exit from Togo, the line continues south into Ghana.
Ghana
The Prime Meridian crosses eastern Ghana from the Burkina/Togo border in the north down to the Atlantic coast at the Gulf of Guinea. The line passes through the Volta Region and the Greater Accra area, exiting the African continent at the coast near Tema, just east of Accra. Tema's port — Ghana's largest — handles most of the country's container trade. Accra itself is at 0°12′ W, only about 23 km west of the meridian, making it the closest national capital city to 0° longitude.
The Royal Observatory at Greenwich: where 0° longitude was set
The Royal Observatory at Greenwichsits on a hill in southeast London at 51°28′40″ N. Founded in 1675 by Charles II to improve astronomical methods of finding longitude at sea, the observatory housed Britain's most precise meridian instruments — particularly the Airy Transit Circle, installed in 1851 by Astronomer Royal Sir George Airy. The instrument's sighting line, projected vertically through the observatory's telescope axis, became the Greenwich Meridian and — in 1884 — the Prime Meridian for the entire world.
Today, a 30-metre brass strip set into the cobblestones of the observatory courtyard marks the historical meridian. At night, a green laser beam shines from the building into the sky along the line. Visitors can stand with one foot in the Eastern Hemisphere and one in the Western — although, as discussed below, the actual GPS zero is about 102 metres further east. The observatory is now part of Royal Museums Greenwich and a UNESCO World Heritage Site.
The 1884 International Meridian Conference in Washington, D.C. drew delegates from 25 nations. Greenwich was selected by a vote of 22 in favour, 1 against (San Domingo, now the Dominican Republic), and 2 abstentions (France and Brazil). France continued to publish charts using the Paris Meridian as a parallel reference until 1911, when it formally adopted Greenwich. The conference also defined the Universal Day starting at midnight Greenwich, which became the basis for all civil time worldwide.
The IERS Reference Meridian: 102 metres east of the brass strip
Visitors who stand on the Greenwich brass strip with a GPS receiver discover something odd: their phone reports a longitude of about 5.31 arc-seconds west (~102.5 metres) of 0°. The brass strip and the modern zero of longitude are not the same line.
The reason is geodesy. The historical Greenwich Meridian was defined astronomically by sighting transits of stars with the Airy Transit Circle — a method that depends on the local vertical (the direction a plumb line hangs). Earth's gravity is not perfectly uniform; small mass anomalies in the crust deflect the vertical by a few arc-seconds depending on location. At Greenwich, the deflection happens to be about 5.3 arc-seconds.
Modern geodetic systems — particularly the World Geodetic System 1984 (WGS84) used by GPS — use a geocentric reference, not a local astronomical one. The zero of WGS84 longitude passes through Earth's centre of mass and the IAU-adopted celestial pole, not through the Airy instrument's sighting line. The difference is the 102-metre offset. Today this modern zero is called the IERS Reference Meridian, and it is the line every GPS, every geographic-information system, and every satellite navigation product treats as 0° longitude. The brass strip remains the historical reference and the cultural one — but not the operational one.
The Prime Meridian and time zones
The Prime Meridian is the centre of UTC+0 (formerly Greenwich Mean Time). Every other time zone on Earth is defined by its offset from the meridian — each 15° of longitude east or west of 0° corresponds, on average, to one hour of time difference (because Earth rotates 360° in 24 hours = 15° per hour).
Among the 8 countries the Prime Meridian crosses, the actual time zones used are a mix:
- United Kingdom — GMT (UTC+0) in winter, BST (UTC+1) in summer.
- France, Spain — CET (UTC+1) in winter, CEST (UTC+2) in summer. Both countries use a time zone that is one hour ahead of their solar time at 0° longitude — a legacy of WWII alignment with Berlin.
- Algeria — CET (UTC+1) year-round. Aligned with Western Europe rather than its African neighbours.
- Mali, Burkina Faso, Togo, Ghana — all use UTC+0 (the same as winter UK time), with no daylight saving.
Greenwich Mean Time itself was superseded in 1972 by Coordinated Universal Time (UTC), which is based on atomic clocks rather than astronomical observation. UTC is held within 0.9 seconds of mean solar time at the Prime Meridian; the difference is bridged by inserting leap seconds roughly every 18-24 months. In casual usage GMT and UTC are treated as identical, though they technically differ by up to a second.
Null Island: where the Prime Meridian meets the Equator
At the point 0°N 0°E, the Prime Meridian crosses the Equator. The intersection sits in the Gulf of Guinea, in the Atlantic Ocean, about 615 km south of the coast of Ghana — the closest land. There is no actual island. The point is marked by the Soul Buoy (a NOAA-PMEL ATLAS weather buoy deployed in 2009), which serves as the visible reference for the location.
The name Null Island arose in the GIS and data-engineering community. When software fails to geocode an address — or a record has missing or zero coordinates — the result is often defaulted to (0, 0). Mapping these mis-coded records onto a globe places them all at the same spot, just south of Ghana. Hence the joke that Null Island is where bad data goes. Despite having no land, it is one of the densest concentrations of erroneous geocoding records on Earth.
Antarctica: the Prime Meridian's southern endpoint
After crossing the Atlantic Ocean from Ghana to about 70° S, the Prime Meridian meets the coast of Antarctica at Queen Maud Land, the Norwegian-claimed sector of the continent. The line then crosses the Antarctic ice sheet to the South Pole, where it meets every other meridian on Earth.
Several research stations operate near the meridian on the Antarctic side: the German Neumayer III station sits at 70°40′ S, 8°16′ W (about 200 km west of the meridian); the South African SANAE IV is at 71°40′ S, 2°50′ W; and the Norwegian Troll station at 72° S, 2°32′ E sits on the meridian's eastern side. From the South Pole, the Prime Meridian runs back northward up the antimeridian (the 180° line), forming a single great circle through both poles.
Related tools and resources
For the antimeridian on the opposite side of Earth — the line that mostly defines the International Date Line — see our International Date Line tool. For the major parallels of latitude, see the Equator (which intersects the Prime Meridian at Null Island), Tropic of Cancer, Tropic of Capricorn, Arctic Circle, and Antarctic Circle.
For other geographic-coordinate tools: find your latitude and longitude with the latitude/longitude finder, locate your antipode on the opposite side of Earth (every point's antipode is on the antimeridian), or convert between coordinate formats with the GPS coordinate converter.
Frequently asked questions about the Prime Meridian
What is the Prime Meridian?
The Prime Meridian is the line of 0° longitude — the universal reference for longitude on Earth, against which every other longitude (east or west) is measured. It runs from the North Pole through Greenwich, England, southward through Europe and West Africa, across the Atlantic, and on to Antarctica. By international agreement at the 1884 International Meridian Conference, the line was set to pass through the Royal Observatory in Greenwich.
What countries does the Prime Meridian pass through?
The Prime Meridian passes through 8 countries: the United Kingdom, France, Spain, Algeria, Mali, Burkina Faso, Togo, and Ghana. North of the UK the line crosses the Arctic Ocean; between Spain and Algeria it crosses the Mediterranean Sea; and after Ghana it crosses the Atlantic Ocean before reaching Antarctica. The total land traversed is about 4,500 km — Algeria has by far the longest stretch.
Where is the Prime Meridian on a world map?
On any standard world map, the Prime Meridian is the vertical line that splits the map roughly in two — running through Western Europe (the UK, France, Spain), down through Western Africa (Algeria, Mali, Burkina Faso, Togo, Ghana), and continuing through the Atlantic to Antarctica. It defines the boundary between the Eastern Hemisphere (positive longitudes, to the right) and the Western Hemisphere (negative longitudes, to the left).
Why is the Prime Meridian in Greenwich, England?
Greenwich was chosen at the 1884 International Meridian Conference in Washington, D.C. because the Royal Observatory there had been the basis of British nautical charts and because the United States had already adopted Greenwich for its own railway time zones. Of 25 countries voting, 22 chose Greenwich; France abstained and continued to use the Paris Meridian for some purposes until 1911. By the early 20th century, Greenwich was the universal reference for longitude and time worldwide.
What is 0° longitude?
Zero degrees longitude is the meridian against which all other longitudes are measured. By definition, the Prime Meridian sits at 0° longitude. Going east of the line increases longitude up to +180°; going west decreases it down to -180°. The +180°/-180° meridian on the opposite side of Earth is the antimeridian, which forms the basis of the International Date Line.
How long is the Prime Meridian?
The Prime Meridian is 20,037 km (12,450 miles) long — the same length as every other meridian on Earth, and exactly half of the polar circumference. Together with its antimeridian (the 180° line), the Prime Meridian forms a great circle through both poles. About 4,500 km of the Prime Meridian crosses land; the rest is ocean and Antarctic ice.
What is Greenwich Mean Time (GMT)?
Greenwich Mean Time is the mean solar time at the Prime Meridian — the longitude at which solar noon occurs at 12:00 GMT on the equinoxes. From 1884 until 1972 it was the world's primary time standard. In 1972 GMT was superseded by Coordinated Universal Time (UTC), an atomic-clock-based standard that drifts no more than 0.9 seconds from GMT before a leap second is inserted. In casual British usage, GMT and UTC are still treated as equivalent.
What is Null Island?
Null Island is the informal name for the point at 0° latitude, 0° longitude — where the Prime Meridian crosses the Equator. It sits in the Gulf of Guinea in the Atlantic Ocean, about 615 km south of the coast of Ghana, the closest land. There is no actual island — only a buoy (Soul Buoy) that has marked the spot since 2009. The name became popular among GIS analysts because mis-coded geocoding records often default to (0, 0), so 'Null Island' is where bad data 'lives.'
Does the Prime Meridian cross the United States?
No. The United States lies entirely west of the Prime Meridian — its easternmost point (West Quoddy Head, Maine) is at 66°57′ W. The line of 0° longitude crosses Western Europe, then Western Africa, and never approaches the Americas. The closest the Prime Meridian comes to North America is Greenland, which it does not touch (Greenland's easternmost point is at 11°W).
What is the IERS Reference Meridian and why is it 102 metres east of Greenwich?
The International Earth Rotation Service (IERS) Reference Meridian is the modern zero of longitude used by GPS, GIS, and satellite navigation. It sits 102.5 metres east of the original Greenwich line. The offset arises because the historic Greenwich Meridian was determined astronomically by sighting transits with telescopes, which were affected by local gravity (the deflection of the vertical caused by Earth's slightly irregular gravitational field). When modern geodesy switched to a satellite-based reference (WGS84), the new zero corresponded to Earth's true geocentre rather than the local astronomical vertical at Greenwich. So the brass strip at the Royal Observatory marks the historic meridian; your phone's GPS shows you crossing 0° longitude about 102 m further east.
What time zone is the Prime Meridian in?
The Prime Meridian sits at the centre of UTC+0 (formerly GMT). The 8 countries the meridian passes through use a range of time zones depending on local conventions: the UK uses GMT/BST; France and Spain use CET/CEST (+1 in winter, +2 in summer); Algeria uses CET (+1 year-round); Mali, Burkina Faso, Togo, and Ghana all use GMT/UTC+0. Time zones are derived from the Prime Meridian — each 15° of longitude east or west of it adds or subtracts one hour.
How is the Prime Meridian different from the Equator?
The Prime Meridian is a meridian (a line of constant longitude running pole-to-pole); the Equator is a parallel (a line of constant latitude running east-west). The Equator is fixed by Earth's axis of rotation and is the same on every planet. The Prime Meridian is set by international agreement and is unique to Earth — there is no natural feature requiring it to pass through Greenwich. The two lines intersect at 0°N 0°E (Null Island), in the Atlantic Ocean about 615 km south of Ghana.
Data sources and methodology
The Prime Meridian is defined by international convention as the line of 0° longitude passing through the Royal Observatory in Greenwich. The IERS Reference Meridian, used by GPS and modern geodesy, sits 5.31 arc-seconds (about 102.5 metres) east of the historical line. Country and continent polygons are from Natural Earth 1:110m; intersection geometry uses Turf.js; the basemap is OpenFreeMap Liberty rendered on a globe by MapLibre GL JS. Greenwich and 1884 conference history are sourced from Royal Museums Greenwich and the proceedings of the International Meridian Conference. The IERS offset is documented in the IERS Conventions (2010) and the WGS84 specification.