To the 1st century BC

The geographers of Miletus: 6th century BC

Nothing is known of the map of the world supposedly produced in Miletus by Anaximander in the mid-6th century BC. But by the end of the century, also in Miletus, another geographer writes a book of which sufficient details survive for his ideas to be reconstructed. He is Hecataeus.

Like most early mapmakers, Hecataeus puts the most important place at the centre of the world. For medieval Christian cartographers this is Jerusalem. For Hecataeus it is the Aegean Sea, on the east coast of which stands Miletus.

The shape of the world according to Hecataeus has a geometrical simplicity. It is a flat circle, with a continuous ocean forming the rim. The circular land mass is divided into two parts by an almost unbroken stretch of water linked with the ocean on the west at the straits of Gibraltar, then running east the length of the Mediterranean, through the Black Sea and (after a short land bridge) into the Caspian Sea, which joins the ocean on the east.

The semicircle of land above this belt of water is Europe, while the semicircle below is Asia. The part west of the Nile has the subsidiary name of Libya, standing in for Africa.

Hecataeus is at the end of a pioneering century of Greek science in Miletus, which lies to the east of mainland Greece. At the same period a new centre of Greek scientific speculation is being developed far to the west, in the Pythagorean tradition of southern Italy.

Greek philosophy is strongly associated with Athens, because of Socrates, Plato and Aristotle. But scientific history testifies rather more to the colonial spread of Greek culture round the Mediterranean. Ionia and Samos, Italy and Sicily, Alexandria; these are the places where Greeks will establish the rational traditions of western science.

A grid before its time: 2nd century BC

One of the most rigorous of Greek scientists, the astronomer Hipparchus, foresees in the 2nd century BC the requirements of a modern map. He is critical of mapmaking efforts by his Greek contemporaries, based on measurements taken on the ground. Instead he proposes a grid of 360° of latitude and of longitude (a number relating back to Babylonian systems), on which places will be plotted according to astronomical readings taken on location.

The necessary instruments of measurement (in particular for the accurate recording of time) are not available to Hipparchus. But his bold idea prefigures the principle of scientific cartography.

Artemidorus: c.100 BC

Artemidorus, a younger contemporary of Hipparchus, is exactly the type of cartographer criticized by the older man. Born in Ephesus, he spends years travelling round the coastal areas of the Mediterranean, making his own measurements between places and noting down distances already measured by others. Late in his life Artemidorus settles in Alexandria and writes eleven books encapsulating his discoveries.

One of several Greek geographers undertaking such activities at the time, the name of Artemidorus acquires special distinction only because of an accidental discovery in the late 20th century.

Artemidorus' works are lost in their entirety. He has been known only through the use of his books by Strabo, a Greek author of the 1st century BC who makes a compilation of geograpical knowledge.

But in 1998 fragments of a papyrus scroll are brought to the attention of scholars. Pieced together, it turns out to be Artemidorus' account of Spain, one of the scenes of his personal travels. Of particular interest is the fact that it contains a map - unfinished, and impossible to relate to a particular region, but showing roads, rivers and settlements in an attempt at a realistic spatial arrangement. As the first example of the kind of map now in everyday use, it will ensure the fame of the previously obscure Artemidorus.

A Roman road map: 1st century BC

The emperor Augustus Caesar puts a close colleague, Marcus Agrippa, in charge of a project to map the Roman roads - amounting to some 50,000 miles. A team of surveyors takes almost twenty years to complete the project.

The end result is a master map, carved in marble and displayed on a wall in Rome. Portable copies are made from this, for the use of soldiers and officials travelling round the empire, and this requirement dictates the shape of the map. It is long and thin, suitable for rolling up as a scroll.

A surviving late copy in the Library of Congress, known as the Peutinger Table, is 22 feet long and just 13 inches high. The details shown make no attempt to reflect the spacial reality on the ground. As with a modern map of an underground railway system, they are purely schematic. The Mediterranean, centre of the Roman world, is like a long canal with routes branching off it.

But for the first time in the history of map-making, over a vast region, a traveller at a crossroads can discover with confidence where he will come to if he turns left, turns right or carries straight on.

1st - 15th century

Imperial science and a great map of China: AD 721-801

The extent of the imperial Chinese bureaucracy under the T'ang dynasty makes possible an unusually thorough scientific project (echoing, for a different purpose, the brave amateur experiment of Eratosthenes 1000 years earlier). In 721 the emperor sets up nine research stations, across a span of more than 2000 miles, from Hue in the south to the Great Wall in the north.

For four years each station measures the sun's shadow at noon on the summer and winter solstice. It is an elegant experiment in that no difficult synchronization is required. The shortest and longest shadows at each place are the correct answers, providing invaluable information for cartographers.

A famous map of 801 - a landmark in cartography - no doubt makes use of the nine points of latitude scientifically established in the experiment of 721-5. It is a map of the Chinese world, produced for the T'ang emperor by Chia Tan.

Chia Tan's map is on an ambitious scale, measuring about 10 by 11 yards. It charts the entire T'ang empire and extends its range into the barbarian world beyond China's borders, showing the seven main trade routes with other parts of Asia.

Mappa Mundi: 13th century

The medieval form of map known simply as Mappa Mundi ('map of the world') features in many manuscripts, particularly in the 13th century. Of about 1000 surviving versions some are small illustrations in bound volumes; others are impressively large. The Mappa Mundi kept in Hereford cathedral measures 64' by 54'.

All follow the same cartographic principle, based on Christian rather than geographical considerations.

In the convention of a Mappa Mundi the world is shown as a flat circle (even though well known to be a sphere). At the centre is Jerusalem; at the top, in the place of honour, is paradise presided over by Jesus. From this the alignment of the map follows in an inevitable hierarchy.

The holiest part of the map is with Jesus at the top; and the holiest point of the compass is the east (the position of the altar in a church). The eastern continent, Asia, must therefore occupy the top half of the map. Jerusalem, the site of the Crucifixion in west Asia, falls conveniently in the exact centre. In a straight line due west to the bottom of the map, as if suspended from Jerusalem, is the Mediterranean.

With the Mediterranean as a vertical dividing line in the lower half of the circle, the position of the other two known continents is fixed. Europe becomes the bottom left quarter, Africa the bottom right.

They are neatly separated from Asia by two waterways, dividing the circle horizontally. To the left of centre, the Black Sea and the river Don; to the right of centre, the Nile. So the waterways form a neat T-shape in the bottom half of the surrounding O, in this most schematic of map conventions. Dragons and monsters conveniently fill up the spaces in which there are no known geographical features.

Portolan charts: 14th century

The experience of practical navigators begins to prevail in maps produced from about 1300, showing the Mediterranean, the Black Sea and the Atlantic coast. Known as portolan charts, they contain more accurate detail than any previous maps. They are criss-crossed by lines joining the main harbours.

These lines tell sailors what course to set on their recently introduced navigational aid, the Magnetic compass. With the accuracy made possible by the compass, feedback from the navigators in turn improves the charts. But this scientific approach to mapmaking is about to suffer a setback, with the European rediscovery of Ptolemy.

Ptolemy and the Renaissance: 15th century

In the gradual spread of ancient Greek texts to medieval Europe, manuscripts of Ptolemy become known by 1400. His account of world geography is widely available after it is translated into Latin in 1410.

With the arrival of printing later in the century, a world map based on Ptolemy's information is a natural project for the publishers. The first printed version, done from engraved copper plates, appears in Bologna in 1477. The projection of the map is redrawn and made clearer in the 1482 German edition, printed in Ulm from wood blocks.

The Ptolemaic map shows the known world, from the Atlantic coast in the west to China and India in the east. India stretches on through what we now call Indonesia, to reach the edge of the map below China. The supposed ocean separating Europe from China and India is the unseen region behind the map.

Luckily for the story of exploration, this ocean is assumed to be relatively small (Ptolemy greatly reduces the more accurate figure for the circumference of the earth arrived at by Eratosthenes). The unseen ocean is small on the world's First globe. And it is on this same assumption that Columbus sails west, just fifteen years after the first printed edition of Ptolemy, confident that he will soon reach the coast of India or China.

Another Ptolemaic error is disproved by the explorers just a few years later. Even though Herodotus reported that a Ptolemy had sailed round the southern tip of Africa, the Ptolemaic map shows south Africa extending east through terra incognita to join up with India in the far East, making the Indian Ocean a vast inland sea.

In 1497 Phoenician fleet makes his way round the Cape of Good Hope, pioneering the sea route to India which he reaches in 1498. Rarely until the 20th century has new technology, in this case the printed map, been so rapidly outdated.

The first globe: AD 1492

One of the most unfortunate innovators in the history of invention is Martin Behaim, the creator of the world's first globe - made in Nuremberg in 1492.

His idea is excellent. A globe is the only accurate way of representing the surface of the earth. His misfortune is to base his globe on Ptolemy (who postulates a single ocean between Spain and China) and to achieve his three-dimensional version of this notion in the very year in which it is disproved - by Columbus reaching America. But Behaim shows the reason for Columbus's confidence in sailing west. The distance on his globe between Spain and China is only half what it should be.

16th - 20th century

Problems of projection: 16th century AD

The European discovery of America and of the Pacific coincides with an increase in ocean travel and with the new Printing techniques of woodcut and engraving. The result is a great demand for maps which can be cheaply produced and which, unlike a globe, will take little space - lying flat, and capable of being folded or even bound into book form.

The printed map is in its vigorous infancy during the 16th century. But a globe remains the only accurate way of representing the land masses on the surface of the spherical earth. How are the newly discovered facts of world geography to be represented on a flat surface?

The problem is real, and in a real sense insoluble. Imagine a rubber globe, hollow like a football. The information on its surface is accurate. But try cutting the globe in half and laying each half out flat, as on a page. It is impossible to do so. Distortion is inevitable. The particular distortion chosen is known as the map's projection. One of the best known is that used by Gerardus Mercator.

His framework is far from new. The grid system of latitude and longitude dates back to Hipparchus in the 2nd century BC, and the prime meridian (or 0° longitude) has run through the Canaries since the second century AD, placed there by Ptolemy. But Mercator's projection is based on new scientific principles.

Mercatow's projection and atlas: AD 1569-1595

Mercator publishes in 1569 a map of the world specifically stated, in its title, to be intended as an aid to navigation. It is laid out on the projection now known by Mercator's name, though it has been used by one or two others before him.

Mercator's projection has the effect of greatly enlarging territories as they recede from the equator. India, for example, appears smaller than Tierra del Fuego. The Moghul emperor Jahangir is understandably displeased at the diminutive size of his empire when the British ambassador, Thomas Roe, presents him with a copy of Mercator's world map.

The distortion of Mercator's projection is a benefit to navigators. By gradually lengthening the lines of longitude towards the poles, Mercator achieves a matching scale for longitude and latitude in every section of the map (the northern degrees of latitude, being shorter in reality, are exaggerated on a regular grid). A compass course can be plotted at the same angle on any part of Mercator's map. As a result marine charts still use this projection.

From 1569 Mercator devotes himself to a vast project, producing a series of maps of Europe which compare Ptolemy's version with improvements based on modern knowledge (much as Vesalius has to measure his own anatomical discoveries against the yardstick of Galen).

By the time of his death Mercator has either published or prepared large engraved maps, designed for binding into volume form, of France, Germany, Italy, the Balkans and the British Isles.

A year after his death, in 1595, Mercator's son issues the entire series under the title Atlas sive Cosmographicae Meditationes ('Atlas, or cosmographic meditations'). It is the first collection to bear the title 'atlas'. Probably based on the Greek mythological character Atlas, whose task is to support the heavens, the name becomes the standard European word for a volume of maps.

Chronometer: AD 1714-1766

Two centuries of ocean travel, since the first European voyages of discovery, have made it increasingly important for ships' captains - whether on naval or merchant business - to be able to calculate their position accurately in any of the world's seas. With the help of the simple and ancient Astrolabe, the stars will reveal latitude. But on a revolving planet, longitude is harder. You need to know what time it is, before you can discover what place it is.

The importance of this is made evident when the British government, in 1714, sets up a Board of Longitude and offers a massive £20,000 prize to any inventor who can produce a clock capable of keeping accurate time at sea.

The terms are demanding. To win the prize a chronometer (a solemnly scientific term for a clock, first used in a document of this year) must be sufficiently accurate to calculate longitude within thirty nautical miles at the end of a journey to the West Indies. This means that in rough seas, damp salty conditions and sudden changes of temperature the instrument must lose or gain not more than three seconds a day - a level of accuracy unmatched at this time by the best clocks in the calmest London drawing rooms.

The challenge appeals to John Harrison, at the time of the announcement a 21-year-old Lincolnshire carpenter with an interest in clocks. It is nearly sixty years before he wins the money. Luckily he lives long enough to collect it.

By 1735 Harrison has built the first chronometer which he believes approaches the necessary standard. Over the next quarter-century he replaces it with three improved models before formally undergoing the government's test. His innovations include bearings which reduce friction, weighted balances interconnected by coiled springs to minimize the effects of movement, and the use of two metals in the balance spring to cope with expansion and contraction caused by changes of temperature.

Harrison's first 'sea clock', in 1735, weighs 72 pounds and is 3 feet in all dimensions. His fourth, in 1759, is more like a watch - circular and 5 inches in diameter. It is this machine which undergoes the sea trials.

Harrison is now sixty-seven, so his son takes the chronometer on its test journey to Jamaica in 1761. It is five seconds slow at the end of the voyage. The government argues that this may be a fluke and offers Harrison only £2500. After further trials, and the successful building of a Harrison chronometer by another craftsman (at the huge cost of £450), the inventor is finally paid the full prize money in 1773.

He has proved in 1761 what is possible, but his chronometer is an elaborate and expensive way of achieving the purpose. It is in France, where a large prize is also on offer from the Académie des Sciences, that the practical chronometer of the future is developed.

The French trial, open to all comers, takes place in 1766 on a voyage from Le Havre in a specially commissioned yacht, the Aurore. The only chronometer ready for the test is designed by Pierre Le Roy. At the end of forty-six days, his machine is accurate to within eight seconds.

Le Roy's timepiece is larger than Harrison's final model, but it is very much easier to construct. It provides the pattern of the future. With further modifications from various sources over the next two decades, the marine chronometer in its lasting form emerges before the end of the 18th century. Using it in combination with the Sextant, explorers travelling the world's oceans can now bring back accurate information of immense value to the makers of maps and charts.

Improvements: 18th - 20th century AD

Once the basic information about the world's landscape is broadly known, improvements in mapmaking become those of greater accuracy, clarity and detail.

A strong impulse towards better surveying and mapmaking comes from the demands of the military. Britain's national cartographic agency admits as much in its title. It is established in 1791 as the Ordnance Survey ('ordnance' being an old-fashioned word for artillery). With a threat of invasion from France during the 1790s, it is not surprising that detailed maps of Kent are the first to be printed.

Advances in surveying make it possible to calculate with accuracy the height of mountains and later even the depth of oceans. Places of the same altitude can be plotted, and recorded in the form of contour lines. By the late 20th century satellites add a new dimension. Powerful lenses in orbit above the earth record the tiniest details on the planet's surface, plotting even the changing patterns of weather or vegetation.

Improvements in colour printing make it increasingly possible to publish this wealth of information in complex form. And digital technology brings an added flexibility in the use of maps on computer screens.
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