The untrue projections develop from the true projections in consideration of one or more special additional conditions. Thus the 3 charcteristic properties of the true projections will disappear wholly or in part.
In this case the third property of the true projections, namely the rectangularity of the grid lines, is mainly affected. This is of particular mathematical importance concerning the local distortion values of a map, but will not be deepened here. To this the interested reader can find advanced informations in the (mathematical) literature. Important keywords are: maximum distortion values, area distortion and angular deformation, ellipse of distortion, Tissot's Indicatrix.
Analog to the true projections the untrue projections are also called non-conical projections. We generally differentiate
|The additional term pseudo means that the accordant untrue projections often are based on true projections.|
The differential-geometrical properties of the untrue projections are important too, but the equal-area projections dominate here.
The untrue projections are often used for an overall view of the Earth.
Advanced descriptions and explanations are offered in the program
|forward to the true projections ...|