Standard Points and Lines in Map Projections

Abstract

In order to be able to read the information a map conveys, we must be familiar with the distribution and size of the inevitable distorsions. Otherwise, our knowledge will be deficient or even wrong. The paper first defines the terms standard point and standard line. The standard point is the point where the inevitable distortions caused by mapping are equal to zero. This definition can be visually interpreted as a Tissot distortion ellipse that becomes a unit circle. After that, it is natural to say that the standard line is composed of standard points. A large number of examples show that the map projection does not have to have standard points at all, but that it can have one such point, two such points or a whole line of standard points. In the latter case, it can be parallels, meridians or lines parallel to the image of the middle meridian, as is the case with the Gauss-Krüger or transverse Mercator projection.