The fundamental procedure behind all cartography is surveying. This involves the precise measurements of distances and directions on the earth’s surface. To facilitate large scale surveying accurately and quickly over large areas, several distances between pre-selected points are measured precisely. These are called baselines, from which a series of triangles are laid out. This process, called triangulation, is the basis of most surveying.
The invention of photography truly revolutionized surveying and map making. For the first time accurate and detailed maps were possible by a relatively quick process. This was accomplished through aero-surveying, which is surveying from aerial photographs with the aid of special instruments such as stereoplotters. Aero-surveying greatly facilitated the making of accurate, finely detailed contour maps.