3-11.  In this projection, meridians are straight lines and parallels are concentric circles.  See Figure 3-12.    Figure 3-10  Polar Stereographic Projection: Secant SECANT PLANE ELLIPSOID Figure 3-11  Origin of Projection b.  Secancy of the Ellipsoid.  The Polar Stereographic Projection is normally considered to be tangent to the ellipsoid.  However, distortion is introduced when the curved surface of the ellipsoid in the vicinity of one of the poles is projected onto a plane.  In order to reduce that distortion the plane is placed secant to the ellipsoid at approximately 81° 07' North and South Latitude.  This establishes a circle in each zone which is common to the ellipsoid and the plane and has no distortion. 0° 20° 40° 60° 0° 90° 90° 180° 60° 60° 30° 30° 120° 120° 150° 150° 80° Figure 3-12  View of Secant Plane c.  Distortion of Lines.  Figure 3-13 shows a cross-section of the ellipsoid and the secant plane made by passing a plane through a polar region of the ellipsoid.  Line A'P'D' represents the plane of projection; line APD is the surface of the ellipsoid. Note that a line on the ellipsoid which lies within the circle formed by the secant condition (latitude greater than 81° 07') is longer than the same line when it is projected on the plane (BP is longer than BP').  Note also that a line on the ellipsoid which lies outside the DRAFT 3-8 Figure 3-13  Line Distortion and Scale Factor in the Polar Stereographic Projection A' A P' P D' D Scale Factor: 1.0   Scale Factor:   0.994 Scale Factor: 1.0   B C LATITUDE:  81° 07' LATITUDE:  81° 07' POLAR AXIS