Leading lights and markers are usually used in the approaches to harbours or in channels where maneuvering room is very restricted.

Their purpose is to guide vessels clear of dangers or down the best channel. They are shown on the chart by a line drawn through them called a leading line. The line is full for a part of its length and then becomes a dotted line. This signifies that this is advisable to keep on it only so far as the full line extends. The dotted line merely guides the eye to the objects which are to be kept in transit.

The names of the objects and their true bearings from seaward when in transit are written along the line drawn through them. The compass bearing of the marks in transit must be compared with the transit bearing marked on the chart. This will provide one with the compass error.

Leading lights and markers.