In radar plotting, OA stands for what?

• A. Own actual position
• B. Targets relative motion line
• C. Ocean area
• D. Orbital angle

Answer: (B)

In radar plotting, the important idea is to understand how a target moves relative to your own ship. When you plot everything on a relative-motion chart, you look at the target’s apparent path as seen from your ship. The line that represents that apparent path—the direction and pace at which the target seems to move relative to you—is called the targets relative motion line. This line is what you use to assess how range and bearing to the target are changing over time, which in turn helps you judge collision risk and predict future positions (like CPA and TCPA).

So OA stands for the targets relative motion line. It’s distinct from your own position (which would be described in terms of your own coordinates), from any notion of ocean area, or from orbital concepts that don’t apply to civilian/maritime radar plotting.