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Tissot's Indicatrix

Tissot's indicatrix is a graphical means for the depiction of the amount and direction of distortion inherent in a map projection transformation. Invented by French mathematician Nicolas August Tissot, the elliptical figure is the result of a theoretical pointsized circle of unit radius on the globe or spheroid having gone through the map projection, and so having been distorted in size and shape.

Indicatrixes are normally shown as open circles or ellipses on a projected map and are repeated at regular intervals of latitude and longitude so that their collective pattern communicates to the map user the overall pattern of projection distortion. The ellipses show orientation, since their axes are in the directions of, and in proportion to, the maximum and minimum map scales at the ...

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