What is Line Of Position or LOP ?

The line of position

A line of position (LOP) is a line established by observation or measurement on which a vessel can be expected to be located. A vessel can be at an infinite number of positions along any single LOP. In piloting, an LOP may be established by a measured bearing to a known and charted object, or by an alignment of two visible and charted objects, or by a measured distance from a charted object.

In the case of bearings, LOPs are straight lines. In the case of distances, LOPs are circles, and sometimes referred to as circles of position (COP). LOPs are used in this text to refer to both. These methods for determination of LOPs are discussed below. LOPs can also be determined by electronic means, such as radar.