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SURVEYING
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SURVEYING , the technical See also:term for the See also:art of determining the position of prominent points and other See also:objects on the See also:surface of the ground, for the purpose of making therefrom a graphic See also:representation of the See also:area surveyed. The See also:general principles on which surveys are conducted and maps computed from such data are in all instances the same; certain See also:measures are made on the ground, and corresponding measures are protracted on See also:paper on whatever See also:scale may be a convenient fraction of the natural scale. The method of surveying varies with the magnitude of the survey, which may embrace an See also:empire or represent a small See also:plot of See also:land. All surveys See also:rest primarily on linear measurements for the See also:direct determination of distances; but linear measurement is often supplemented by angular measurement which enables distances to be determined by principles of See also:geometry over areas which cannot be conveniently measured directly, such, for instance, as hilly or broken ground. The nature f the survey depends on the proportion which the linear andcombination of both. See also:History.—The art of surveying, i.e. the See also:primary art of See also:map-making from linear measurements, has no See also:historical beginning. The first See also:rude attempts at the representation of natural and artificial features on a ground See also:plan based on actual measurements of which any See also:record is obtainable were those of the See also:Romans, who certainly made use of an See also:instrument not unlike the See also:plane-table for determining the See also:alignment of their roads. See also:Instruments adapted to surveying purposes were in use many centuries earlier than the See also:Roman See also:period. The Greeks used a See also:form of See also:log See also:line for recording the distances run from point to point along the See also:coast whilst making their slow voyage from the See also:Indus to the See also:Persian Gulf three centuries B.C.; and it is improbable that the See also:adaptation of this form of linear measurement was confined to the See also:sea alone. Still earlier (as See also:early as 1600 B.c.) it is said that the See also:Chinese knew the value of the loadstone and possessed some form of magnetic See also:compass. But there is no record of their methods of linear measurements, or that the distances and angles measured were applied to the purpose of map-making (see COMPASS and MAP). The earliest maps of which we have any record were based on inaccurate astronomical determinations, and it was not till See also:medieval times, when the See also:Arabs made use of the See also:Astrolabe (q.v.), that nautical surveying (the earliest form of the art) could really be said to begin. In 1450 the Arabs were acquainted with the use of the compass, and could make charts of the coast-line of those countries which they visited. In 1498 Vasco da Gama saw a See also:chart of the coast-line of See also:India, which was shown him by a See also:Gujarati, and there can be little doubt that he benefited largely by See also:information obtained from charts which were of the nature of See also:practical coast surveys. The beginning of land surveying (apart from small plan-making) was probably coincident with the earliest attempts to discover the See also:size and figure of the See also:earth by means of exact measurements, i.e. with the inauguration of See also:geodesy (see GEODESY and EARTH, FIGURE OF THE), which is the fundamental basis of all scientific surveying. See also:Classification.—For convenience of reference surveying may be considered under the following heads—involving very distinct branches of the art dependent on different methods and instruments t: 1. See also:Geodetic triangulation. 2. Levelling. 3. Topographical surveys. 4. See also:Geographical surveys. I. GEODETIC TRIANGULATION Geodesy, as an abstract See also:science dealing primarily .with the dimensions and figure of the earth, may be found fully discussed in the articles GEODESY and EARTH, FIGURE OF THE; but, as furnishing the basis for the construction of the first framework of triangulation on which all further surveys depend (which may be described as its second but most important See also:function), geodesy is an integral See also:part of the art of surveying, and its relation to subsequent processes requires See also:separate See also:consideration. The part which geodetic triangulation plays in the general surveys of civilized countries which require closely accurate and various forms of mapping to illustrate their See also:physical features for military, See also:political or fiscal purposes is best exemplified by reference to some completed See also:system which has already served its purpose over a large area. That of India will serve as an example. The See also:great triangulation of India was, at its inception, calculated to satisfy the requirements of geodesy as well as See also:geography, because the latitudes and longitudes of the points of the triangulation had to be determined for future reference by See also:process of calculation combining the results of the triangulation with the elements of the earth's figure. The latter were not then known with much accuracy, for so far geodetic operations had been mainly carried on in See also:Europe, and additional operations nearer the See also:equator were much wanted; the survey was conducted with a view to See also:supply this want. Thus high accuracy was aimed at from the first. Primarily a network was thrown over the See also:southern See also:peninsula. The triangles on the central See also:meridian were measured with extra care and checked by See also:base-lines at distances of about 20 apart in 1 The subject of See also:tacheometry is treated under its own heading. 5. Traversing, and fiscal or See also:revenue surveys. 6. Nautical surveys. Additional information and CommentsThere are no comments yet for this article.
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