User:Datumizer/Sandbox/Surface of latitude

Fig. a. A naive approach to specifying a surface of latitude would be to cut through the Earth in a straight line to form a plane.

Fig. b. However, it would be more accurate to say that on a spherical Earth, a circle of latitude forms a cone pointing toward the Earth's center.

Fig. c. But the Earth deviates from a perfect sphere, and instead roughly forms the shape of an ellipsoid (greatly exaggerated in this image), causing this cone to become truncated. This representation corresponds to "geodetic latitude".

Figure d is apparently not true. See: here.