On which chart projections is a great circle approximately a straight line?

• A. Mercator only
• B. all projections except Mercator and Transverse Mercator
• C. all projections except Lambert Conformal
• D. all projections except Polar stereographic

Answer: (B)

A great circle is the shortest path on a sphere, and how it appears on a map depends on how the projection distorts distance, direction, and shape. On Mercator and Transverse Mercator, distortions grow rapidly away from the central lines, so a long segment of a great circle typically curves on the map rather than appearing as a straight line. In contrast, projections like Lambert Conformal Conic and Polar Stereographic are designed to preserve shapes and directions more consistently over their standard areas, so a portion of a great circle often looks like a near-straight line within those charts. Since these projections generally keep great-circle paths close to linear over practical chart extents, the statement that a great circle is approximately a straight line on all projections except Mercator and Transverse Mercator is the best fit. Exact straight-line representation only happens in a projection like the gnomonic, which isn’t among the options, so this is a useful practical rule of thumb.