[Telepathic Intruder]

Circles can be calculated using either Cartesian coordinates or trigonometry.

[Travis McGee]

Great Circle charts are a lot of fun. Draw a straight line between origin and destination, then plot lats and lons derived from the GC along the way on your normal charts to achieve your great circle.

Of course, if you are just using your GPS chart plotter, as most are, this is an automatic function.