small circle

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small circle A circle on the surface of a sphere whose centre is not coincident with the centre of the sphere, so that a plane whose circumference is a small circle does not bisect the sphere. In a stereographic projection a small circle projects on to the plane of projection as a circle whose centre lies inside the primitive circle. If the small-circle plane is horizontal it will project as a circle smaller than the primitive circle but concentric with it. If it is vertical it will project as an arc, concave towards the centre of the primitive circle.

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