How to flatten a face to avoid distortion (make an ngon planar) I created a kind of procedural modeled ground (rocks desert like), with some decimate modifiers to have a really crazy topology.

The result is nice, except for some ngons faces that contains some weird normals, due to the elevation difference of several vertices:



How to avoid this? My first guess is to "flatten the face, but I can't figure out the way to do this operation.

I must specify that the face is not perpendicular to the Z axis, so a zero-Z-scaling (S Z 0) won't work here.
You can scale along the normal.

Set the Transform orientation to Normal in 3D view > Header:



Then press SZZ0.