A position line or line of position (LOP) is a line (or, on the surface of the Earth, a curve) that can be both identified on a chart (nautical chart or aeronautical chart) and translated to the surface of the Earth. The intersection of a minimum of two position lines is a fix that is used in position fixing to identify a navigator's location.

There are several types of position line:

• Compass bearing – the angle between north and the line passing through the compass and the point of interest
• Transit – a line passing through the observer and two other reference points
• Leading line – the line passing through two marks indicating a safe channel
• Leading lights – the line passing through two beacons indicating a safe channel
• Sector lights – the lines created by masked colored lights that indicate a safe channel