Size matters

Cartography - Peter Barber goes in search of Truth and Reality

Most of us have a touching faith in maps. "To put something on the map" is to establish its very existence. Increasingly, people figuratively "map out" phenomena to establish a factual baseline for decision-making. The mathematical accuracy of the features depicted tends to be regarded as the sole determinant of a map's quality. Mathematical accuracy is equated with absolute truth. Maps become "The Truth" and even "The Reality". In 1542, courtiers complained that the Holy Roman Emperor Charles V was being diverted from proceeding with the invasion of France because he regarded his enticing map of the country as a substitute; while in the film The Great Dictator, the dictator Hynkel, played by Charlie Chaplin, plays with globes as though he were thereby actually dominating the world.

Yet even the most scientifically produced modern maps have only a tenuous relationship to truth and reality, and many map-makers would not consider that they were doing their job if every feature on their map was depicted with total mathematical accuracy. Indeed, maps could be said to be, in several respects, the most convincing fictions around. However, paradoxically, it is precisely this ability to ignore or distort aspects of reality that is essential for their utility. It is the same feature - their subjectivity - that makes maps so fascinating to a layman with no particular interest in geography.

Clearly, it is impossible to reproduce total reality in reduced form - so you have to choose what features, out of the myriad possibilities, you wish to represent. Then, if it is sufficiently important for your intended purpose, you may choose to exaggerate its size. You will add symbols instead of realistic representations, and words by way of clarification. So subjectivity comes in by the front door.

This is well illustrated by the recently published London Photographic Atlas. Compare the aerial photographs on the first 295 pages with the conventional A-Z-style maps that follow. You will immediately see that the roads on the maps are much clearer than those on the last group of photographs, even though a single map covers twice as much ground. You can read the street names, but most of the buildings and trees are missing. Indeed, on the standard A-Z, the streets are shown much bigger than they really are; and even on conventionally printed Ordnance Survey maps, the size of major roads is exaggerated. Fair enough, you may say, because you are primarily interested in routes. But it's not Truth or Reality. And what if you want some quite different information, such as the number and size of local parks, which are made smaller on the A-Z to make space for roads? It would be interesting to know how many perfectly pleasant, relatively cheap neighbourhoods are ignored by house-hunters who use the wrong sort of map when choosing an area to live.

It is subjectivity - also known as purpose - not mathematical accuracy, that necessarily lies at the heart of cartography. When you look at a map, first find out its intended purpose and then look at the cartographer's bias. This is often difficult to detect, because we generally share the map-maker's scale of values - we agree on what is important. But when a map is created by a nonconformist, the subjectivity of the accepted view often becomes apparent. Compare the crusading world map produced for Unesco with a conventional Mercator projection world map. The first utilises the Peters projection, which shows the true proportions of the land masses, in the process demonstrating the actual size of the countries in the developing world, but distorts their shape. The other exaggerates the sizes of Europe and North America, but shows the true shapes of the land masses. Neither projection is true, given the impossibility of truthfully depicting the total reality of the ball that is the earth on a flat piece of paper. The map-makers chose the projection that most effectively meets their purpose - or appears to "prove" their argument.

Subjectivity also enables old maps to provide unique insights into the mentalities of ages past. Take the example of one of the best-known early images of London, produced by Georg Braun and Franz Hogenberg in Frankfurt in 1572. It presents an attractive image, combining a measured ground plan with views of the principal buildings. For these reasons, it has frequently been reproduced in coffee-table books. Yet take a look at the image as a whole. It gives no hint of the reality of the grotesque overcrowding and sickness that, we know from other sources, prevailed in Tudor London. Why are none of the halls of the livery companies named, while several aristocratic town houses are? Why is the royal barge shown at the mathematical centre of the map on a Thames that is grossly inflated in size? Above all, why do the text panels talk about London's dependence on trade for its wealth and on the virtues of the Hanseatic League, a loose but powerful confederation of northern German trading cities, whose London headquarters, the Steelyard, is named in small capitals? The map is, in fact, a piece of Hanseatic propaganda. It is intended to depict a city made prosperous by a seaborne trade fostered by the merchants of the Hansa, a city ruled by queen and ministers rather than by English merchants through the livery companies.

The original map was probably created by the merchants of the Steelyard at a time when they were struggling to restore the extensive privileges of which they had recently been stripped, largely because of the opposition of the English merchants. It is only in this context that its veracity can properly be judged. There are alternative and very different-looking maps of the same city that could have been drawn at the same time, such as plans of the overcrowded dwellings created by Ralph Treswell for landlords keen to maximise their income from rents.

Set against this variety of images, objective, photographic truth, even if attainable, seems dull - and far from useful.

The BBC Radio 4 series The Secrets of Maps is broadcast from 9.30am to 9.45am on Tuesdays until 20 February

Peter Barber is the deputy map librarian at the British Library

This article first appeared in the 12 February 2001 issue of the New Statesman, Exclusive: how Labour could lose