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Tissot's indicatrix
See Also:
distortion,
projection
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[map projections]
A graphical representation of the spatial distortion at a particular map location. The indicatrix is the figure that results when a circle on the earth's surface is plotted to the corresponding point on a map. The shape, size, and orientation of an indicatrix at any given point depend on the map projection used. In conformal (shape-preserving) projections, the indicatrix is a circle; in nonconformal projections, it is an ellipse at most locations. As a visual aid, indicatrices convey a general impression of distortion; as mathematical tools, they can be used to quantify distortion of scale and angle precisely. The indicatrix is named for Nicolas Auguste Tissot, the French mathematician who developed it. 
