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The point on the surface of the sphere is depicted on the cylinder in this way. All

points on the sphere except the poles can in principle be depicted on the

cylinder, and all points on the cylinder correspond to one and only one point on

the surface of the sphere.

In practice, areas around the poles will occupy a disproportionately large area
and be heavily drawn on the map. The Mercator projection is therefore not

particularly suitable for mapping around the poles, which are therefore often

omitted (see the map above).

9.4.1.5 Gnomonic projection

The sphere is placed on a plane and the center of the sphere is chosen as the

projection point. A point on the sphere is depicted by drawing a straight line from

the projection point through the point on the plane (see the figure).

The figure shows that the

northern hemisphere and

the southern hemisphere

must be depicted separately.

The point where the image

plane touches the sphere can be chosen freely.

The gnomonic projection has the following properties and shortcomings:

- A straight line between two points on the map shows the shortest path
between the points. That is, great circles are depicted as straight lines.

- Not conformal

- Does not display areas correctly

- The center is displayed correctly, but distortion increases rapidly away from

the center

- Only distances measured from the center are correct

Flyveteori PPL(A)(UL)/LAPL Henning Andersen, Midtjysk Flyveskole© 2025 818