In 1838 the triangulation of Scotland was resumed; and the survey of Ireland hav ing been finished in 1840, surveys for a six-inch map were begun for the northern por tions of England which had not been mapped on the one-inch scale, In connection with this map the base-line on Salisbury plain was remeasured with great accuracy in 1849, and its length found 36577.8581 feet. Iu 1841 some secondary operations for a map of Scotland, also on a six-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 six-inch scale on which only it was published, a committee of the house of commons (lord Eleho's) recommended the six-inch maps to be stopped, and the one-inch map completed as speedily as possible. This change pro duced much discussion as to the relative value of the one-inch and six-inch scales then in use, and the expediency of adopting a still larger scale as more valuable to the pub lic. Circulars were issued, asking the opinion of various public bodies, and of scien tific and practical men, as to the proper scale for a great national survey. The great preponderance of opinion was in favor of a scale of 1-2500 of nature, or nearly one inch to the acre. This scale was therefore ordered by a treasury minute of May 18, 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 (Dec. 1857), and ordered to be resumed by another treasury minute (Sept. 11, 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 min ute of May 8, 1855, be extended to those portions of the United Kingdom that have been surveyed on the scale of one-inch to the mile only. This recommendation has DOW been adopted by the government, and the survey is at present proceeding on the following scales: Towns having 4,000 or more inhabitants are surveyed on a scale of 1-500 of the linear measurement, which is equivalent to 126.72 in. to a mile, or 411 ft. to an inch; Parishes (in cultivated districts) 1-2500 of the linear measurement, equal to 25.344 in. to a mile, or one sq.inch to an acre; counties on a scale of 6 in. to a mile; kingdom, a general map one inch to a mile.
The sheets of the one-inch map join together, so as to form a complete map of the whole kingdom. This is true also of the sheets of each county on the six-inch scale, and of each parish on the 1-2500 scale, but the sheets of different comities and parishes are not connected. The 1-2500 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 six-inch scale, and published on the pne-inch scale.
In the report on the progress of the ordnance survey, it is stated that in England, up to the end of 1876, an Rica of 28,654 sq.m. (the area of England being 58,000 sq.m.) had been surveyed; to the end of 1877, the area was 29,839 sq.miles. Since 1854, when the survey on the scale of 1-2500th began, the English counties that had been surveyed were Durham, Westmoreland, Northumberland, Cumberland, Middlesex, Kent, Essex, Sur rey, Hampshire, and Sussex, also (it haying been decided that the mineral districts should take precedence of the rest of the kingdom) Cheshire, Flintshire, and Denbigh shire, with portions of several other counties.
In Scotland, up to the end of 1876, (out of a total area of 31,000 sq.m.) had been surveyed, of which 451 sq.m. were done in 1876. The survey of the whole of Scotland was completed in 1377. At the end of 1875 maps on the 1-2500 scale had been
published for an area of 11,107 sq.miles. On the six-inch, scale an area of 21,332 sq.m. had been published; 15,930 sq.m. of the one-inch map have been completed and pub lished with hills.—In Ireland, as stated, the six-inch maps have been long published, and are now in process of revision. A one-inch map of the whole in outline has been published, and is being completed by the addition of hills. The engraving of hills in the remainder is also being proceeded with. In all the three kingdoms, plans of many of the towns on the 10 and 5 ft. 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 one 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 1-50,000, or about 1+ inch to the mile, would'have been preferable for the small map; in which ease a scale of 1-10,000 of nature, or about 61 in., might have been chosen for the intermediate, instead of the six-inch scale selected at first for mere local purposes in Ireland. Be this as it may, the arguments in favor of the one-inch map are, that it is the most convenient both as a general and traveling map. For gen eral views of the structure of'a country, the distribution and relations of its mountains, plains, valleys, and rivers, the one-inch is admitted to be superior td the six-inch, and thus better adapted in the first instance for laying 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 measurement of small distances; it is in some respects a generalized picture, and not a correct plan. The six-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 six-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 one-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 one-inch map. Most of the purposes of the six-inch plans are attained in a still more perfect manner front the 25-inch plans or cadastrat survey. This la,st name is taken from the French cadastre (a register of lands), and is defined (in the 1?ecueil des kris, etc.) 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 gen eral taxes may be raised, and roads, railways, canals, and other public works, laid out and executed.