Tissot indicatrix
As Tissot's indicatrix (after the French mathematician Nicolas Auguste Tissot ) is called distortion ellipses, with the help of map projections on their distortion characteristics can be checked out.
Circles of the same size are drawn around different points (usually a grid of points with equidistant coordinate values) on the earth's surface. After leveling in the map, different deformations can occur in the circles. Then the most important properties of the map network design can be assessed.
- In conformal designs, all distortion ellipses are circles.
- In equal-area designs all distortion ellipses have the same area size.
- At length loyal designs distortion ellipses along the length fidelity equal radii. Most maps are only true to length along the parallels or meridians .
Behrmann's equal-area sectional cylinder design: All distortion ellipses have the same area size.
Correct angle Mercator projection : All distortion ellipses are circles.
Mediating Robinson projection : This map projection is neither true to area nor true to length or angle.
