Which projection characteristic has rays that originate from the center of the Earth?

• A. Gnomonic projection
• B. Stereographic projection
• C. Orthographic projection
• D. Mercator projection

Answer: (A)

Rays originate from the center of the Earth describes the gnomonic projection. In this setup, each point on the Earth’s surface is projected along a line that passes through the planet’s center onto a plane that is tangent to the sphere. Because the projection lines come from the center, great circles—the shortest paths on a sphere—become straight lines on the map, which is why this projection is useful for plotting routes. However, only a portion of the globe is shown (the hemisphere around the tangent point), and distortion grows rapidly toward the edges.

Other projections use different origins for their projection lines. Stereographic projection projects from the opposite point on the sphere onto the tangent plane, preserving angles and circles but not the straight-line mapping of great circles. Orthographic projection uses rays from infinitely far away, giving a view akin to a globe seen from space and not the center-based mapping. Mercator uses a cylinder and has a distinct distortion pattern, especially in the polar regions, and does not involve projecting from the Earth's center.