Excerpt from Surveying: A Plane Table Manual Since it is a representation in miniature, the distance between any two points on the map is a certain definite fraction of the distance between the same points in nature. This ratio is called the scale. Each point, besides being projected on a horizontal plane, has its height, either within, above, or below a level surface, in some way indicated. The level surface adopted for the map is called the datum plane, and the representation of the variations in the vertical element, the modeling of the country, is called the relief. About the Publisher Forgotten Books publishes hundreds of thousands of rare and classic books. Find more at www.forgottenbooks.com This book is a reproduction of an important historical work. Forgotten Books uses state-of-the-art technology to digitally reconstruct the work, preserving the original format whilst repairing imperfections present in the aged copy. In rare cases, an imperfection in the original, such as a blemish or missing page, may be replicated in our edition. We do, however, repair the vast majority of imperfections successfully; any imperfections that remain are intentionally left to preserve the state of such historical works.