Surveying

Surveying is the science of measuring the shape and size of any portion of the earth's surface in order that a map or plan may be drawn. The area to be surveyed is divided up into a number of triangles, whose sides and angles are measured: the area can be calculated from the figures so obtained, and a plan can be made by reproducing the triangles on a reduced scale. The simplest appliances for the purpose consist of a chain and cross-staff or optical square. By means of the former the lengths of the sides of a triangle may be determined, and with the aid of the latter a perpendicular may be drawn from the bases to the apex of the triangle. From the observed lengths of the sides and the perpendicular, the area of the triangle can be ascertained, and it is evident that the area of a plot of land is the sum of the areas of the triangles into which it has been divided. For more extended surveys optical instruments for measuring angles are used. Three points are selected, and the distance between two of them is measured by a chain or otherwise. The angles between this baseline and the lines joining its extremities with the third point are then measured, and from these three measurements the area of the triangle may be calculated, as also the lengths of the two sides. Either of these sides may now be used as the base of a second triangle, and this process of triangulation may be repeated to any required extent.