Secant plane

A secant plane is a plane containing a nontrivial section of a sphere or an ellipsoid, or such a plane that a sphere is projected onto. Secant planes are similar to tangent planes, which contact the sphere's surface at a point, while secant planes contact the surface along curves.

Animation showing the circular secant planes of the ellipsoid

The two-dimensional representations of secant planes are secant lines, the lines that join two distinct points on a curve.


Comparison of tangent and secant cylindrical, conic and azimuthal map projections with standard parallels shown in red

Secant planes are used in map projections. The secant plane intersects a globe along a small circle with no distortion, forming a standard parallel which has true scale.[1]

See alsoEdit


  1. ^ "Map projection - types and distortion". Retrieved 2016-11-02.

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