Brian Hooker

New Zealand

A multiplicity of prime meridians


Brian Hooker

© Brian Hooker 2006. The text that follows is copyright. Apart from any fair dealing for the purposes of private study, research, criticism or review, no part may be reproduced without prior permission.

The purpose of this article is to trace the development of the prime meridian from the time of its earliest mention or insertion in maps until the final acceptance of Greenwich as the prime meridian at the International Meridian Conference of 1884.

The need for a prime meridian became necessary after western explorers started to venture west and south-west from bases on the Iberian Peninsula in the fifteenth century. For centuries, the inability to measure longitude had been the great obstacle to accurate long-distance navigation. Navigators needed to know their position east or west of a base line as well as north and south of the equator.

The measurement of latitude had been practised since before the Christian era and had been used at sea since the days of Prince Henry the Navigator who promoted voyages of discovery around the 1450s. Determination of longitude was a very different matter. While latitude could be reckoned from the equator, for longitude there was no definite datum. A prime meridian provides a precise datum in an imaginary line passing around the earth, over the North and South Poles and through a nominated position.

The development of successful methods for determining longitude is beyond the scope of this commentary but those who seek elucidation of the subject should refer to Dava Sobel’s book, Longitude.


Up until 1884, the selection of a prime meridian was based on patriotism, an idea of the cartographer, misconception, or a general geographical theme. As well as Greenwich, Lizard Point, and St Paul’s Cathedral in England some of the other prime meridians used between the sixteenth and late nineteenth centuries, were: Toledo, Paris, Cracow, Uranibourg, Copenhagen, Goes (Netherlands), Amsterdam, Pisa, Augsberg, Rome, Ulm, Tübingen, Bologna, Rouen, St Petersburg, Cadiz, Pulkowa, Naples, Christiania (Oslo), Rio de Janeiro, Philadelphia, Washington DC.

From about the beginning of the eighteenth century some countries selected as their zero meridian the state observatory.

Ancient concepts

The first attempt to insert a prime meridian in a map was probably made by Eratosthenes who lived around 220 BC. This renowned Greek mathematician and geographer became superintendent of the great library at Alexandria the capital of ancient Egypt. The works of Eratosthenes have perished but we know through contemporary accounts that he prepared a map with a zero meridian that passed through Alexandria. Eratosthenes mistakenly believed that this meridian also passed through the island of Rhodes and Syene (present-day Aswan in southern Egypt). Hipparchus, an eminent astronomer, who lived at Rhodes around 160 to 125 BC, fixed the geographical position of places by latitude and longitude; he used Rhodes as a prime meridian probably also in the false belief that the same meridian passed through Alexandria and Syene. No further progress took place for 300 years until the time of Marinus of Tyre and his successor Claudius Ptolemy.

Ptolemy the great Alexandrian astronomer and mathematician lived in the second century AD. In his best known work Geographia, Ptolemy discusses geodesy and the mathematics of cartography, and lists the latitude and longitude co-ordinates of 8,ooo places. He gathered these from ancient maps or estimated them from travellers’ reports. The extent of Ptolemy’s indebtedness to Marinus is unknown but we know that Marinus produced geographical data without maps.

Believing that the known world occupied half the circuit of the globe, Ptolemy numbered his meridians from zero degrees to one-hundred and eighty degrees from west to east, starting from the Canary Islands the remotest western land at the time reported. No maps have survived from Ptolemy’s time but we shall see later that Ptolemy’s data lived on to provide fifteenth century map publishers with basic instructions for map-making.

It was generally believed in ancient times that the westernmost part of Europe was the Sacred Promontory – present-day Cabo de São Vincente. Both Marinus and Ptolemy established their prime meridian 2 degrees 30 minutes west of Cabo de São Vincente which coincided with the western extremity of the Canary Islands; but in a modern map these islands are portrayed about eight degrees west of Cabo de São Vincente.

Following Ptolemy no further advances were made in regard to the prime meridian for over a thousand years. However, the Arabs kept the flame of geographical knowledge alight and in the early Arab world, the problem of the prime meridian was not unknown. Some Arab geographers used as their prime meridian a line supposedly drawn midway between the remotest point east and the remotest point west through a mythical city named Arin later assumed to be ten degrees east of Baghdad.

The age of discovery

Following the discovery of America, Pope Alexander VI settled the rival claims of Spain and Portugal, in 1493, by issuing the famous Bull establishing a line of demarcation. This line ran from north to south a hundred leagues west of the Azores, to the west of which the Spaniards were authorised to explore, and to the east of which the Portuguese received the monopoly of discovery. A year later – 1494, under the terms of the Treaty of Tordesillas, the line was moved farther westward and fixed at 170 leagues west of the Cape Verde Islands. A landmark chart that includes the Tordesillas Treaty Line as the prime meridian is Diogo Ribeiro’s chart of 1529 now preserved in the Vatican Library. Ribeiro, an eminent cartographer of his era was in the service of Spain from 1519.

Ptolemy’s Geographia was first printed with maps at Bologna in 1477; this was about a thousand years after the great geographer first put forward his views. Included with this edition are twenty-six maps including a world map, which extends across 180 degrees of longitude. The prime meridian in this map passes through the Canary Islands. It has been claimed that the printed maps of Ptolemy led to Columbus’s voyage to America. In any case, the discoveries of Columbus gave a great impetus to map- and globe-making and hastened the need for maps with meridians including a prime meridian.

One of the earliest if not the earliest extant globe to show a prime meridian post Columbus is the so-called Green or Quirini, globe now preserved in the Bibliothèque Nationale de France, Paris. In this globe believed to date from around 1513-1538, the prime meridian is made to pass through the Cape Verde Islands, a group referred to as Insule Portugalensium invente anno Domini 1472. Probably, earlier globes followed Ptolemy’s lead and featured a prime meridian passing through the Canary Islands.

A world chart apparently made in 1529 by Girolamo Verrazano, an Italian navigator sent by Francis I, King of France, to explore the New World, includes two sets of meridians. The original set is in ink with the prime meridian passing through the west point of La Palma in the Canaries, a second set in pencil with longitudes unmarked, is based either upon the west point of Madeira or upon the centre of Flores in the Azores.

Gerard Mercator was the most important cartographer of the sixteenth-century and one of the giants of early cartography. In 1538, Mercator produced at Louvain his first world map on the recently invented double cordiform projection. Mercator’s map was an improved version of a map of 1531 in the same projection by Orance Finé. Following Ptolemy’s lead, Mercator drew his prime meridian vaguely through the centre of the Canary Islands. However, he became better known in the early years of his career for the production of globes. In 1541, he produced his famous forty-one centimetre terrestrial globe and drew his prime meridian precisely through Fuertaventura, one of the easternmost of the Canary Islands. This work was praised at the time as unsurpassable. At this time Mercator was still under the influence of Ptolemy to a large degree.

A factor that strongly influenced the prime meridian for the next three hundred and thirty years was the idea a place or places existed where the compass showed no variation. The variation of the compass from true north could be found by taking a bearing on the Pole Star and noting the declination of the needle east or west of the pole. The theory of the relation of variation to the magnetic pole had been formulated by cosmographers early in the sixteenth century and was based on reports that circulated subsequent to Columbus’ voyage. One of the first men to suggest the use of the variation in finding the longitude was Ruy Faliero, whose manuscript treatise on navigation was taken with him by Magellan on his voyage of circumnavigation in 1519-1522.

By the 1550s Mercator’s views had changed. An essay in the form of a letter addressed to Charles V, the Holy Roman Emperor in 1553, contains evidence that Mercator supported the idea of matching the place of zero variation with the prime meridian. In 1569, he produced his famous world map, drawn in the projection that was the elucidation of a mathematical conundrum – portrayal of the surface of a sphere on a flat sheet of paper. On this map, he drew the prime meridian through the Cape Verde Islands because, as he explained in a legend within the map, he had consulted an experienced pilot, Francis of Dieppe who told him that the compass needle did not vary in the  islands of Sal,Boa Vista and Maio. Others believed that this also occurred at sea between Terceira and São Miguel and at Corvo in the Azores. An examination of the area in Mercator’s map shows that he was either confused about the correct positions of these various islands or he thought the magnetic meridian was a meridian great circle. His line passes through the islands of São Miguel and Santa Maria, in the Azores, one-and-a-half degrees west of Ferro in the Canary Islands and then through Sal, Boa Vista, and Maio in the Cape Verde Islands. A modern map reveals a considerable difference in longitude between the islands in the various groups. It was much later before anyone realized that the variation underwent a slow world-wide change, or that isogonic lines were mostly circuitous curves.

Preserved in the National Library at Stockholm is a world map, dated 1542, in the form of two hemispheres of globe gores. Of particular interest in this map drawn by Alonzo de Santa Cruz, Spanish Cosmographer Royal to Charles V, is the meridian drawn west of the island of Faial in the Azores. Twenty degrees west of this line Santa Cruz has drawn the Tordesillas Treaty Line mentioned earlier.

Abraham Ortelius’s Theatrum orbis terrarum first appeared at Antwerp, in 1570; this was the first  printed collection of maps in the structure of a modern atlas. Included is a world map drawn on a cordiform projection and published originally in 1563. The prime meridian passes through the islands of São Miguel and Santa Maria in the Azores. This world map appeared in numerous editions of Ortelius’ atlas including pocket-size editions over the next forty-two years.

A significant stage in the development of sea charts was reached in 1584 with the publication of Waghenaer’s sea-atlas Spieghel der Zeevaerdt. Lucas Janszoon Waghenaer was a celebrated Dutch hydrographer and pilot of Enkhuizen. His work was translated into English in 1588 as The Mariners’ Mirrour. Only one chart in the collection has the longitude marked upon it and the prime meridian in this print passes through the Canary Islands between Gomera and Tenerife.

Petrus Plancius the notable Dutch navigational authority and cartographer was the scientific force in 1602 behind the formation of the Dutch East India Company. Plancius endorsed the use of islands in the western Azores for the prime meridian and in particular Santa Maria. He made a special study of the magnetic variation technique and to assist and promote his cause he arranged for observations concerning variation to be carried out during the first and second Dutch voyages to the East Indies and, later, he analysed the data obtained.

Another giant of his era in cartography was the Flemish cartographer and engraver Jodocus Hondius. Of particular interest in a discussion on the prime meridian is a legend in Hondius’ terrestrial globe of 1601. This legend deals extensively with the variation of the compass and concludes with the words:


  We have begun our longitudes not as Ptolemy did
from the Fortunate [Canary] Islands but from those called Azores because there the compass needle points due north.

Hondius does not identify the island he selected but an examination of the globe shows that the prime meridian passes through the island of São Miguel in the Azores. In his great world map first published in 1598 and drawn in Mercator’s projection Hondius drew his prime meridian through the sea between the islands of Corvo and Faial in the Azores.

The prime meridian concept based on compass variation was beginning to crumble by the early part of the seventeenth century although it lingered on well into the eighteenth century; it was rejected or found to be illusionary by several writers in the early 1600s. We have seen in the previous paragraph that Hondius supported the idea but Willem Jansz [Blaeu] the founder of the foremost seventeenth-century publishing house of Blaeu started to lose faith in the idea early in his career. If Blaeu was in two minds about selecting Corvo as his prime meridian in his two-sheet world map of 1604 he hedged his options to some extent by incorporating extra meridians, some of which were in use at the time as prime meridians. One supplementary meridian passes beside the west side of São Miguel, and another passes through Lizard Point, Cornwall.

By 1608, Blaeu had unreservedly rejected the concept of a prime meridian based on compass variation. Proof of Blaeu’s understanding of the subject is provided by the fact that after 1611 he often figured as an expert witness at official inquiries into proposed solutions for the problem of determining longitude. Blaeu gradually changed his prime meridian in maps and globes from islands in the Azores, to the Peak of Tenerife in the Canary Islands. In his large 1619 world wall map he explains his reasons for selecting Tenerife in a boxed legend. In addition, in his 1617 sixty-eight centimetre terrestrial globe which also reckons longitude from Tenerife, he includes a legend ridiculing ideas held by others concerning variation of the compass as a guide for fixing their first meridian. In a newly-worded legend in his terrestrial globe of 1622 Blaeu reinforces his choice of Tenerife and adds the interesting comment that he has “differed barely a quarter of a degree from the longitude of the Arabs who selected the extreme western shore of Africa” (i.e. Cape Vert).

During the eighteenth century leadership in cartography and map publishing passed from Amsterdam to France. Louis XIII made the first attempt at standardisation of the prime meridian by a decree of 1 July 1634. He declared that the French should use the meridian passing through the westerly point of the Canary Islands. Unfortunately, no one could determine the longitude of the Canary Islands with any precision and the estimate that Ferro was twenty degrees west of the observatory at Paris turned out to be half a degree in error. In effect, the figure of twenty degrees transferred the prime meridian to Paris.

Throughout the eighteenth century, English charts used randomly the meridian of St Paul’s Cathedral, Lizard Point or sometimes Ferro. John Seller’s 1676 map of Herefordshire was the first to use the prime meridian of London. The Lizard meridian was used not only by English seamen but also by Dutch navigators sailing the channel and proceeding along the coasts of France, Portugal or Spain.

Charles II founded the Royal Observatory at Greenwich in 1675 for the study of navigation and nautical astronomy. This provided the catalyst for its later selection as the prime meridian but Greenwich came into general use by the British only after the Nautical Almanac, prepared by the Astronomer Royal, Nevil Maskelyne commenced publication in 1767. Earlier, maps published by Feardon and Eyes and Thos. Jeffreys used Greenwich. In 1777, Des Barres used the meridian of Greenwich in his Atlantic Neptune.

From about the time of the first publication of Cook’s charts in 1773 supremacy in map publishing was gained by England. Cook’s charts and thereafter Admiralty charts used Greenwich. The office of Hydrographer to the Admiralty was established in 1795 when Alexander Dalrymple was appointed to the position. At this time by far the greatest number of charts issued and used around the world were those of the British Admiralty.

Greenwich by twenty-two ayes

As early as 1800, Pierre Simon Laplace the famous French astronomer and mathematician urged his fellow scientists to consider the idea of an international prime meridian. “It is desirable” he wrote, “that all the nations of Europe, in place of arranging geographical longitudes from their own observatories, should agree to compute it from the same meridian, one indicated by nature herself, in order to determine it for all time to come. Such an arrangement would introduce into the science of geography the same uniformity which is already enjoyed in the calendar …,” What he meant by “one indicated by nature” is unknown.

It was another seventy-one years before an International Congress assembled at Antwerp to discuss the unsolved problems related to geography and cosmography. Delegates from nineteen countries attended but at the start, the atmosphere was tense since the Franco-Prussian war had only just concluded. No great issues were resolved at this first International Congress but much discussion ensued. Tributes were paid to the work of Abraham Ortelius and Gerard Mercator and plans were made for a further meeting at Paris.

The second International Geographical Congress took place at Paris in 1875 and a third meeting occurred at Venice in 1881. Twenty-nine countries were represented. At last progress was being made on the question of an international prime meridian and a uniform standard of time but no conclusions were reached. Already the majority of countries were favouring the idea of a prime meridian passing through the centre of the transit instrument of the Greenwich Observatory. At this meeting, a serious plan was put forward by one of the French delegates for the idea of a metric division of time and arc as well as the calendar. Fortunately this suggestion was not generally supported. Finally, it was decided to hold an international conference to settle differences of opinion on the basic issues associated with time and a universal prime meridian.

An Act of Congress passed on August 3 1882 authorised an International Meridian Conference to be held in Washington DC and all nations were invited to appoint delegates to fix upon a universal prime meridian. “as a common zero of longitude and standard of time reckoning throughout the globe.” Delegates from twenty-five nations met in Washington in October 1884. At the Conference several important principles were established. The meridian passing through the principal Transit Instrument at the observatory at Greenwich was to be the initial meridian.

This resolution fixing the meridian at Greenwich was passed twenty-two to one with France and Brazil abstaining. Among other resolutions passed was one specifying that longitude would be calculated both east and west from Greenwich up to 180 degrees. □


Brown, Lloyd A. The story of maps, New York: Dover publications, 1979.
Crone, G. R. Maps and their makers, London Hutchinson, (4th ed), 1968
Howse, Derek, and Michael Sanderson The sea chart, Newton Abbot: David & Charles, 1973.

Van‘T Hoff, (Introduction to) Gerard Mercator’s map of the world … Rotterdam/’s-Gravenhage, 1961.



In addition, there are a number of informative web sites that are worth searching for.


Images to follow.

The Atlantic Ocean, in Jan Jansson’s  Novus Atlas,Vol V (Amsterdam, 1650). The prime meridian passes through the centre of Corvo in the western Azores.

Novus Orbis (New World) by Francis Gaulle, in Peter Martyr, De Orbo Novo … (Paris, 1587). The prime meridian in this map passes through Toledo in Spain.

Cornwall and the Scilly Isles: Plate XVII of Christopher Saxton’s large map of England and Wales, 1583. Saxton selected as his prime meridian a line passing through the island of Santa Maria in the Azores.

One of the earliest if not the earliest extant globe to show a prime meridian post Columbus is the so-called Green or Quirini globe. In this globe believed to date from around 1513-1538, the prime meridian is made to pass through the Cape Verde Islands.
Courtesy: Bibliothèque Nationale, Paris.

Abraham Ortelius, World map, Antwerp, 1589. This small size map of the world was widely circulated in the Epitome of Ortelius’ Atlas, a popular work for a century. The prime meridian passes through the islands of São Miguel and Santa Maria in the Azores.

Charevoix-Bellin, This map is found in Charlevoix’s, Journal d’un voyage, Paris, 1744. The meridians are reckoned from a prime meridian running through Paris.