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This is why the great circle lines will always be the shortest lines along the earth's

surface.

For our purposes, the difference between a great circle and compass line means
nothing. When we produce maps for our type of flying, VFR over short distances,

we use the Gnomonic projection.

When we do this, a straight line between 2 points will be a great circle line and

thus the shortest distance.

The 2 pictures on the next page show a MERCATOR projection at the top. Here
the parallels of latitude are straight lines.

The shortest distance in this type of projection is not a straight line, as is the case

in the GNOMONIC projection shown below, which is what our maps are.

As you can see from the drawing

here, we have to constantly

change course to fly along the

great circle line (because the great

circle line curves (unless we fly
along a meridian).

In practice, we only measure one

value, namely the middle of the

route in relation to a central

meridian.

On the Mercator projection, a straight line is actually a course line, since it

intersects the meridians (which are parallel lines) at the same angle.

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Flyveteori PPL(A)(UL)/LAPL Henning Andersen, Midtjysk Flyveskole© 2025 821