Tissot's indicatrix

As tissotsche indicatrix is called distortion ellipses, with the help of card network designs can be checked for distortion properties. They were named after the French mathematician Nicolas Auguste Tissot (* 1824, † 1890 ).

To various points (usually a grid of points with equidistant coordinate values ​​) large circles are on the earth's surface drawn level. After Verebnung in the map different deformations can occur in the circles. After that then can be judged the most important features of the card network design.

• In conformal designs all distortion ellipses are circles.
• For equal-area designs all distortion ellipses have the same area size.
• At length-preserving designs, the distortion ellipses have equal radii along the length of loyalty. Most cards are isometrically only along the parallels or meridians.

The tissotsche indicatrix in the conformal Mercator projection; All distortion ellipses are circles.

The tissotsche indicatrix in mediating Robinson projection; This map projection is neither equal area nor conformal or isometrically.

• Mathematical Geography