Every parallel of latitude is represented on a map by the developed circumference of a right cone tangent to the Earth at the parallel of the projection. Which projection is described?

• A. Polyconic
• B. Cylindrical equal area
• C. Stereographic
• D. Mercator

Answer: (A)

Think of shaping the Earth’s surface with a cone for each parallel of latitude. For every latitude, you place a right cone so that it’s tangent to the sphere exactly along that latitude. When you unroll that cone onto a plane, the circle around the latitude—the circumference of the cone at that latitude—becomes a straight line on the map. In this way, every parallel is represented by the developed circumference of a cone tangent at that latitude. This is the hallmark of the polyconic projection, which uses multiple cones (one for each parallel) and unrolls them to the plane.

Other options rely on a cylinder or a plane projection from a point, so their parallels aren’t obtained by developing a tangent cone’s circumference. Cylindrical equal area and Mercator use a cylindrical surface, while stereographic projection maps from a point onto a plane, producing circles rather than the cone-developed straight-line representation described here.