Baseline

Base-line, in Surveying, is a straight line very accurately measured on the tract of country to be surveyed. The position of this line having been fixed, other points may be plotted by simply observing the angles they subtend at each end of the base-line. Thus triangles are plotted, each of whose sides may in turn be regarded as a new baseline. In the Ordnance Survey of England and Wales the base-line was measured on Salisbury Plain, and was some miles in length.