The projections here are neither conformal nor equal-area, and they have curved meridians and parallels.
However, I do not group them with the conventional projections. In that group, I place only projections designed for ease of manual construction. Here, the projections presented are determined mathematically, and this is done in many cases in ways analogous to those used for the equal-area projections of the preceding chapter.
In general, the projections in this section are derived, like Winkel's Tripel projection, by applying mathematical transformations to existing projections. However, there are other types of projection in this group, such as the Laskowski Tri-Optimal Projection.