In the method of the invention, we apply appliqués of constant Gaussian curvature to the corresponding areas of comparable curvature.

Gaussian curvature is the product of the two principal curvatures.

A point at which the Gaussian curvature is positive is called an elliptic point.

Now, the Gaussian curvature is the product of these two curvatures.

The points at which the Gaussian curvature is zero are called parabolic.

Put another way, the spherical map cannot be represented as a plane without some sort of distortion — see stereographic projection, Gaussian curvature, and the video below.