THE NATIONAL MAP
By MICHAEL SPENDER
MAP-MAKING, a pleasant and gentle occupation for anyone who likes to be out of doors, is in most countries a soldier's business, though as such remarkable as one of the few activities fostered by War Offices which invigorate a nation's peace-time affairs. When, for instance, a century ago the railways were beginning to spread their network over the country, the Ordnance Maps helped them to find the most profitably graded routes ; and in recent times these maps, selling in ever increasing numbers, have enabled the motorist to plan an enduring series of new and enjoyable tours. Admittedly in the course of the years the survey of the British Isles has been put under the Ministry of Agriculture and Fisheries ; but it is still directed by officers of the Royal Engineers, and by its name it recalls the original significance of the map.
Towards the middle of the eighteenth century the art of war had become so complex that neither troops nor cannon could be properly disposed without using the kind of description of terrain which is a map. Trouble in Scotland at the time of the rising of the Young Pre- tender started the first major piece of mapping to be carried out by the army ; and fear of the consequences of the French Revolution caused the work of the Ordnance Survey proper to be put in hand. Modern gunners hardly trouble to think in terms of the landscape ; they shoot between points on the map where both gun-position and target arc described not by name but by co-ordinates ; the guns are laid in accordance with two sets of x, y and z. The Ordnance Survey maps are nevertheless still precise enough for the most modern weapons ; their foundation is a triangulation which only the best of modern instru- ments and methods could better.
The map-using public is not required to appreciate the subtleties of this kind of precision, where the intrinsic errors of the plan are often less than those arising out of the expansion and contraction of the paper on which the map is printed. But an easy. approach to the significance of geodetic standards of accuracy is to think of the defects which might appear in the map of, say, Skye, as a result of an accumulation of small errors in a series of measurements beginning on Hounslow Heath. The founders of the Survey took the long view in planning their work ; the fact that the framework has been reliable and even the map itself of long standing has meant that the map-using public has in no country been better served than in the British Isles.
Not making maps on the ground, but revising and above all producing them, has for over half a century been the main business of the survey department. There has been time to experiment and select thoSe features of the landscape which are important to the civilian. It must be realised that there is no absolute ideal to be aimed at in drawing a map ; the selection of detail is , always arbitrary, and the features chosen by soldier or airman may not be those required by walker or motorist. To realise how highly stylised a map is, compare it with an air photograph. The camera records that aspect of a landscape which impresses a photo- graphic plate. The consequence is a pattern of light and shade which is often very difficult to disentangle and interpret ; a mass of unimportant information overwhelms the detail which is valuable when printed on the map. Whatever is chosen for eventual presen- tation must usually be conventionalised and exaggerated to show it at all ; even the widest of arterial roads would give too fine a trace on the One Inch scale to be of any use to the map-reader.
The maps now being issued from Southampton make an exceptionally excellent range, of which each, member is suitable to a group of particular purposes. Some small criticisms can, of course, still be made : the new arterial roads ought to be distinguishable from other first class highways ; and obviously more care must be taken in supplying information to be used by the growing class of people who explore our inland waterways. But in most features the British public has in the Fifth (Re- lief) Edition of the One Inch map at once one of the most practical and most beautiful maps ever published. The shape of the land is shown intelligibly, and yet in a way which does not confuse other detail ; and the letter- ing is of great elegance, recalling something of the quality of the Elizabethan county maps by Saxton, the repro- ductions of which by the British Museum now decorate so many homes.
The more surprising it is, then, that in spite of all this excellence the foundations of the national map have to all intents and purposes to be completely resur- veyed. Plainly the reasons for such drastic action cannot be superficial. In fact the defects that make this work necessary are only evident on the larger-scale plans. But a new class of map-user has appeared, as once more the map takes an important part in national development. Under the Town-Planning Acts close on half the area of England and Wales is included under town and country planning schemes. Progress with the draft schemes and official approval of them is impossible without up-to-date maps, for the maps are the basis of all discussion. The Ordnance Survey describes these drawings on the 1 : 25,000 scale, or roughly 25 inches to the mile, not as maps but as plans. Post-War economies have caused the revision of these plans to get very far behind. A crisis has arisen, because the planning committees cannot work unless they know which existing properties are going to be affected by such proposals as new roads or new open spaces. If the town - planning schemes are to go ahead, several thousand plans must be revised rapidly. At the same time another group of users of the plans, the mining engineers, is finding inconvenience through the change of projection at county boundaries, a technical incon- venience exaggerated by .a tendency to error in the same regions.
The trouble with the 25-inch plan is then of two kinds. Firstly there is the immediate need to lay down sufficient detail to assist the town planning schemes. But then comes also the necessity of getting the plan on a single projection for the whole country and correcting the internal errors that have accumulated during a century of copying and transferring. The points which constitute the framework of the national survey have mostly been lost ; and in many cases the records are in disorder. Hence it is that the whole triangulation will during the next years be newly observed, computed and adjusted. A beginning has been made with- the Principal Triangulation and the work can now be seen in progress along the backbone of north and central England. The measurements are made from concrete pillars at the tops of hills ; these stations are visited in turn by lighting and observing parties, for most angles are nowadays measured between illuminated beacons by night.
Thus a network of fixed points is determined and a map begun. The filling in of detail is a task very similar to revision. The old surveyors worked on the ground, making direct measurements of distance with a chain. This procedure is slow and expensive in modern built-up areas, as the local authorities who themselves attempted revision found to their cost. But the century that has elapsed since the first parties of chain-men were sent out has brought the aeroplane. Just how far air-photography will be helpful in revising and renewing the survey of Great Britain is not a matter on which anything authoritative can be said ; but it is an interesting problem.
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