Which projection is best for plotting great-circle navigation routes?

• A. Mercator projection
• B. Gnomonic projection
• C. Polyconic projection
• D. Lambert projection

Answer: (B)

Great-circle routes are the shortest paths on a sphere, so you want a map where those geodesics appear as straight lines. The gnomonic projection does exactly that: it projects points from the center of the globe onto a tangent plane, and any great circle—being a plane through the center—maps to a straight line on that plane. So drawing a straight line on a gnomonic chart directly corresponds to following a great-circle route on the globe. Keep in mind distances and areas get badly distorted away from the tangent point, so this projection is ideal for plotting shortest paths, not for accurate measurement. Other projections preserve shapes or angles or areas, but they don’t turn all great circles into straight lines, which is why the gnomonic projection is the best fit for plotting great-circle navigation routes.