The theory of distortion of map projections developed by N.A. Tissot is briefly discussed. The restrictions imposed on the mapping functions of map projections, which influence the solution of the problem for finding the best projections, are formulated. In particular, an indicator is proposed to identify such a restriction as mutual unambiguity. The issue of converting the azimuth of a direction on an ellipsoid to the grid azimuth of the projection in this direction on a plane is studied in detail. Methods for visual representation of distortions on maps are considered. Along with traditional methods of displaying distortions using isocols and Tissot’s indicatrixes, a method based on symbol-chartsSymbol-charts is proposed.