Why are checkpoints so uneven? Why are there more of them on the edges?

It depends on how the surface was created, the number of control points in each direction, and the degrees of the surfaceâ€¦ How did you create the surface in your image?

Control points for a NURBS surface are in a rectangular array with rows and columns. Each row has the same number of control points and each column has the same number of control points. The number of control points in the rows may be different than the number of control points in the columns. The number of control points on an edge is the same as the number of control points in other rows or columns. There are not more control points on the edges.

A simple variant, a surface of 3 degrees, and 5 control points, this is in the Rebuild window.

The control point spacing which Rebuild uses is because of a choice made when the software was created. There are an infinite number of possibilities for control point spacing and the one you see is the one which was selected.

Okay thank you!