Civil Engineering Association

The object of Topography is to determine the relative positions of points of the earth's surface, that can be referred without error to a tangent plane, and therefore independent of the sphericity of the globe. The operations of a topographical survey, consequently, are two namely, to first project a system of points upon such a tangent plane ; and, secondly, to find the distances of the same above or below the plane; or, in other words, to measure the lengths of the projecting normals. The first process is ordinary surveying; the second, levehng.The results of a topographical survey are laid down in a so-called topograpliical map, which is a representation or complete image of the ground on a reduced scale.

Topographical maps are of the greatest convenience in locating railroads or other roads, in planning irrigation works, draining Avorks, in mining enterprises, in military operations, &c., &c. In a topographical map the configuration of the ground is reduced to an image, which represents to the eye a large area at one glance,which in nature could not be view edbut by many separate inspections ; therefore, the judgment about the relation of the different parts of the work will be a clearer and more intelligent one. This refers especially to mining work, where very frequently the problem occurs, to strike a vein with a tunnel in a certain level. In this problem a correct topographical map will often save the mining company several hundred feet of tunnel work, or, in other words, thousands of dollars.