In which projection are great circles represented as straight lines in all aspects?

• A. Aphylactic
• B. Gnomonic
• C. Stereographic
• D. Orthographic

Answer: (B)

The property comes from projecting from the Earth’s center onto a plane tangent to the globe. A great circle is the intersection of the sphere with a plane that passes through the center, so when you project from the center onto the tangent plane, that circle maps to a straight line on the map. This holds for any great circle within the map’s valid area, though the gnomonic chart only covers within 90 degrees of the tangent point before distances blow up. Other projections do not keep every great circle as a straight line in all directions.