Ordnance Survey.

Chambers's Encyclopaedia, Volume 7: Maltebrun to Pearson, p. 633–635

Ordnance Survey. By this term is understood the various operations undertaken by the British government for preparing maps and plans of the whole kingdom and its parts, the term 'ordnance' being applied from the fact that during its earlier days the survey was carried out under the direction of the Master-general of the Ordnance. The idea of a general map of any portion of the country to be executed by the government was first proposed after the rebellion in 1745, when the want of any reliable map of the northern parts of Scotland was much felt by the officers in command of the royal troops. Its execution was entrusted to Lieutenant-general Watson, the deputy quarter-master of North Britain; but it was mostly carried out by Major-general Roy, an officer of engineers. The drawing, on a scale of 1\frac{1}{2} inch to the mile, was completed in 1755; but, in consequence of the war which broke out in that year, was never published. In 1784, with the object of calculating the difference of longitude between the observatories of London and Paris, a base-line was measured by General Roy, R.E., on Hounslow Heath, from which started a series of triangles extending to Dover. This triangulation was connected with that carried out in France in 1786. The government shortly afterwards decided on having, for military purposes, a general survey on the 1-inch scale of the United Kingdom, and the triangulation carried out by General Roy in the south-eastern counties became the basis of the general triangulation. In 1794 the survey for the 1-inch map was begun, and the first sheet was published in 1801. As the series of principal triangles were extended westwards towards the Land's End, it was thought right to measure another base on Salisbury Plain in 1794; and two base-lines for verification were subsequently measured—one in 1801 at Misterton Carr, and the other in 1806 on Ruddlan Marsh. Though first intended chiefly as a military map, the publication of the survey soon created a desire on the part of the public for better maps, and surveyors were then hired to hasten its progress. This, however, was very slow, the map being at one time entirely suspended during the war in the beginning of the 19th century, and even the parts which were executed, having been done by contract, were found very inaccurate. In this condition the survey of England continued during the first quarter of the century, sometimes delayed by the government from motives of economy, at other times urged on by the county gentlemen, who wished the map either as a hunting-map or for local improvements.

In Scotland the principal triangulation was begun in 1809, but was discontinued in the following year, to enable the persons who had been employed there to carry forward the subordinate triangulation required for constructing the detail maps in England. In 1813 it was resumed, and continued steadily up to 1819; a new base-line having been measured on Belhelvie Links, near Aberdeen, in 1817, and the great sector used at various stations, both on the mainland and in the islands. In 1820 it was again suspended, was resumed in 1821 and 1822, and anew broken off in 1823, the large theodolite being wanted in order to proceed with the principal triangulation in South Britain. In 1824 the survey of Ireland was begun, and nothing more was done in Scotland till 1838, except that some detail surveying for a 1-inch map was continued for a few years in the southern counties. The chief strength of the surveying corps was now transferred to Ireland. A map of that country was required for the purpose of making a valuation which should form the basis of certain fiscal arrangements and other improvements which the social evils and anomalies of Ireland urgently demanded. For this map a scale of 6 inches to the mile was adopted, as best suited for the purposes in view. On this scale the whole map was completed, and published in 1845, though the first portions were in an imperfect form, and needing revision, which was proceeded with in 1873.

The triangulation of Scotland was resumed in 1838, and in 1852 the whole of the primary triangulation of the United Kingdom was completed. It comprises, in all, 250 trigonometrical stations, and the average length of the sides of the triangles is 35.4 miles, the longest being that from Seaw Fell to Slieve Donard, which measures 111 miles. During the triangulation of Ireland a base-line had been measured on the border of Lough Foyle. As a test on the general accuracy of the triangulation the length of this base was afterwards calculated through the series of triangles from the base on Salisbury Plain; the length so found differed from the measured base by only a little more than 5 inches. The distance apart of these two bases is about 360 miles, and their length about 41,641 and 36,578 feet respectively.

The survey of Ireland having been finished in 1840, surveys for a 6-inch map were begun for the northern portions of England which had not been previously mapped on the 1-inch scale. In 1841 some secondary operations for a map of Scotland, also on a 6-inch scale, were begun, but proceeded so slowly that in 1850 only the map of Wigtownshire and some parts of Lewis were completed. Much dissatisfaction having been expressed in Scotland by the press and public bodies as to the slow progress of the map and the 6-inch scale on which only it was published, a committee of the House of Commons (Lord Elcho's) recommended in 1851 the 6-inch maps to be stopped, and the 1-inch map completed as speedily as possible. This change produced much discussion as to the relative value of the 1-inch and 6-inch scales then in use, and the expediency of adopting a still larger scale as more valuable to the public. Circulars were issued, asking the opinion of various public bodies, and of scientific and practical men, as to the proper scale for a great national survey. The great preponderance of opinion was in favour of a scale of \frac{1}{25000} of nature, or nearly 1 inch to the acre. This scale was therefore ordered by a treasury minute of 18th May 1855 (Lord Palmerston's), and though subsequently stopped, in consequence of a motion by Sir Denham Norreys in the House of Commons in June 1857, was again recommended by a royal commission (December 1857), and ordered to be resumed by another treasury minute (11th September 1858). In 1861 a select committee was again appointed, and reported that it is desirable that the cadastral survey on the scales directed by the treasury minute of the 18th May 1855 be extended to those portions of the United Kingdom that have been surveyed on the scale of 1 inch to the mile only. This recommendation was presently adopted by the government, and the survey has been completed on the following scales: Towns having 4000 or more inhabitants are surveyed on a scale of \frac{1}{500} of the linear measurement, which is equivalent to 126.72 inches to a mile, or one inch to 41\frac{1}{3} feet; parishes (in cultivated districts) \frac{1}{25000} of the linear measurement, equal to 25.344 inches to a mile, or one square inch to an acre; counties on a scale of 6 inches to a mile; kingdom, a general map 1 inch to a mile.

The sheets of the 1-inch map join together, so as to form a complete map of the whole kingdom. This is true also of the sheets on the 6-inch and \frac{1}{25} scales of each county, but the sheets of different counties, except when drawn to the same meridian, are not connected. The \frac{1}{25} scale also applies only to cultivated, populous, and mineral districts; the Highlands of Scotland, and other extensive moorland and uncultivated tracts, being only surveyed on the 6-inch scale.

The scale, originally 1 inch to a mile, was increased to 6 inches to a mile when the survey reached Yorkshire and Lancashire; these counties being done on that scale as well as on the 1-inch scale. The remaining counties of England were done on the scale of 25 inches to a mile for cultivated districts, and on 6 inches to the mile for the uncultivated and moorland districts. When England was completed a re-survey was begun on the 25-inch scale of those counties which had only been surveyed on the 1-inch scale. The sheets on the scale of 25 inches to a mile (called parish maps) are reduced by photography, and issued on the scale of 6 inches to a mile (county maps). The 1-inch maps are again reduced by photography from the 6-inch, and are being published in outline only and also with hills.—The survey of the whole of Scotland was completed in 1877, and the maps for the whole area, on either the 25-inch or 6-inch scales, have been published. On the 1-inch scale two editions are published, one in outline only and another with hills.—In Ireland, as stated, the 6-inch maps have been long published, and are now in process of revision, and a survey on the 25-inch scale has been commenced. A 1-inch map of the whole in outline, and, with the exception of a few sheets, an edition with hills have been published. In all the three kingdoms plans of many of the towns on the 10 and 5 feet scale are also published.

The sketch now given of the history of this great national undertaking will show that it has been conducted at different times on different scales and plans, and that the system now pursued was only adopted after much discussion both in parliament and out of doors. The map was originally begun as a military map, and the scale of 1 inch to the mile chosen, without considering whether some other scale would not offer greater advantages. Many now think that a scale a little larger, and an aliquot part of nature, such as \frac{1}{50} or about 1\frac{1}{2} inch to the mile, would have been preferable for the small map; in which case a scale of \frac{1}{100} of nature, or about 6\frac{1}{2} inches, might have been chosen for the intermediate, instead of the 6-inch scale selected at first for mere local purposes in Ireland. Be this as it may, the arguments in favour of the 1-inch map are that it is the most convenient both as a general and travelling map. For general views of the structure of a country, the distribution and relations of its mountains, plains, valleys, and rivers, the 1-inch is admitted to be superior to the 6-inch, and thus better adapted in the first instance for laying out roads, railways, or other extensive public works, or for the publication of a general geological survey. Such a map, on the other hand, is on too small a scale to admit of correct measurements of small distances; it is in some respects a generalised picture and not a correct plan. The 6-inch maps were at first selected in Ireland as the smallest size on which correct measurements of distances and areas could be made. On them every house and field, and almost every tree or bush, might be laid down. Hence they are superior for working out details, as in minute surveys of railways or roads, or the complex geological structure of rich mineral districts. On such sheets, too, a proprietor or farmer may find every field laid down, and the relative heights indicated by contour lines, and may therefore use them for drainage and other improvements. It has also been proposed to use these 6-inch maps as a record of sales or encumbrances of land, thus lessening the cost and simplifying the transfer of property. On the other hand, their size unfits them for most of the purposes for which the 1-inch map is useful, and the contour lines give a far less vivid and correct impression of the physical features of a country than the hill sketching of the 1-inch map. Most of the purposes of the 6-inch plans are attained in a still more perfect manner from the 25-inch plans or cadastral survey. This last name is taken from the French cadastre ('a register of lands'), and is defined (in the Recueil des Lois, &c.) as a plan from which the area of land may be computed, and from which its revenue may be valued. The purposes to which these large plans may be applied are as estate plans, for managing, draining, and otherwise improving land, for facilitating its transfer by registering sales or encumbrances; and as public maps, according to which local or general taxes may be raised, and roads, railways, canals, and other public works laid out and executed. In 1870 the Ordnance Survey was transferred from the control of the War Office to that of the Office of Works, and in 1890 to the newly-instituted Board of Agriculture.

Nearly all civilised states have produced trigonometrical surveys, many of them of great excellence as scientific works. The most important are:

The Coast and Geodetic Survey of the United States, which was authorised in 1807, but not really begun till 1817, is a work of enormous extent, great accuracy, and minute detail. The full organisation of the survey was mainly due to A. D. Bache (q.v.). The general charts are published on a scale of \frac{1}{100} or \frac{1}{4}ths of an inch to a mile; the harbours and ports \frac{1}{100} or \frac{1}{3}ths of an inch to a mile. A vastly greater undertaking, the triangulation of the whole area of the republic, has been more recently begun. The great Trigonometrical Survey of India was commenced in 1832; and the year 1880-81 witnessed the completion of the principal triangulation of all India. The maps are published on various scales, those of the Trigonometrical Survey being on a scale of \frac{1}{100} or '25 inches to a mile, whilst maps on both larger and smaller scales are published for revenue and special purposes.

The Geological Survey of the United Kingdom, though under a different department of government (Science and Art), may be shortly noticed here. The English survey, begun in 1832, was completed on the scale of 1 inch to a mile (solid geology), and the Drift survey proceeded with. The Irish survey was begun in 1840, but was subsequently suspended till 1845. It was completed in 1887, and the whole of the maps are now published. In 1854 the survey was extended to Scotland. The southern half of the country has been completed, and the mapping of the Highlands is now in progress. The surveys are made on the 6-inch maps in the parts of the country where these exist, but the results are published on the 1-inch scale only, except some of the mineral districts, which are issued also on the 6-inch scale. Besides the maps, sheets of sections, horizontal and vertical, with valuable memoirs, and monographs on fossils, are also published; and a general index map, scale 4 miles to an inch, is in progress. A survey of the West Indies has been carried out, and memoirs descriptive of the geology of Trinidad, Jamaica, and British Guiana have been published. The geological survey of Canada and that of India are vast undertakings in progress; also government geological and mining surveys are in progress in the Australian colonies. See the articles CONTOUR LINES, MAP, SURVEYING; Colonel White's Ordinance Survey of the United Kingdom (Edin. 1886).

Source scan(s): p. 0646, p. 0647, p. 0648