SURVEYING, the technical term for the art of determining the position of objects on the surface of the ground, for the pur pose of making therefrom a graphic representation of the area surveyed. The general principles on which surveys are conducted and maps constructed from such data are in all instances the same; certain measures are made on the ground, and correspond ing measures are protracted on paper on whatever scale may be a convenient fraction of the natural scale. The method of sur veying varies with the magnitude of the survey, which may em brace an empire or represent a small plot of land. All surveys rest primarily on linear measurements for the direct determina tion of distances ; but linear measurement is often supplemented by angular measurement which enables distances to be deter mined by principles of geometry over areas which cannot be con veniently measured directly.
History.—It is very probable that surveying had its origin in ancient Egypt. But long before the dynastic period in Egypt, we may imagine that neolithic man was able, like the savages of to-day, to make a rough kind of map based on his journeys, or a primitive plan to show tribal or property boundaries. Apart from such speculations, however, we find, in a Theban tomb of the XVIII. dynasty, a plan of the villa of a great Egyptian noble : in the tomb of one Menna at Thebes, there is a representation on the walls of two chainmen surveying a field of corn : and in Ptolemaic and Roman papyri in the same country, measurements of plots of land are described. That the early Egyptians could carry out measurements with a considerable degree of accuracy, is certain from a study of the dimensions of the Great Pyramid.
In Roman times we meet with the groma, which consists of two pairs of plumb-lines suspended from the ends of two hori zontal rods, at right angles to each other : the use of the instru ment being to lay out lines at right-angles. The metal parts of one of these gromas was found in 1912, in Pompeii. An early groma of the same type, but rougher construction has been found in Egypt. The Romans also used 1 o foot rods, and bronze terminal pieces of such rods have been found at Enns in Austria, the foot in this case being 13.2 inches. The Romans certainly made use of an instrument not unlike the plane-table for deter mining the alignment of their roads. The Greeks used a form of log line for recording the dis tances run from point to point along the coast whilst making their slow voyage from the Indus to the Persian gulf three cen turies B.C. Still earlier (as early
as 1600 B.c.) it is said that the Chinese knew the value of the load stone and possessed some form of magnetic compass. The earliest maps of which we have any record were based on inaccurate astronomical determinations; not till mediaeval times, when the Arabs made use of the astrolabe (q.v.), could nautical surveying really be said to begin. In 145o 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 chart of the coast-line of India, which was shown him by a Gujarati. Plane-tables were in use in Europe in the i6th century and the principle of graphic triangulation and intersection was practised by surveyors in England and elsewhere. In 1615, Wille brord Snell, the Dutch mathematician, measured an arc of meri dian, by instrumental triangulation.