@VA7SDH @ZachWeinersmith
A 3D sphere is not just curved in 3D, it is impossible to map it to a flat 2D space. The sum of internal angles of triangles on its surface will not be 180°. A torus (= donut) on the other hand is curved in our 3D world, but _can_ be mapped to a flat, purely 2D surface. It would be like a computer game where you enter the screen from the left as you enter from the right or fall from the top as you fall through the bottom.