Thanks for your examples, Martin. The intention was to have like a perfect plateau for buildings, like boxes on a surface. This surface is a topography, so that when making a section, the boundary of the building will fit exactly with the boundaries of the plateaus (if the plateaus are so smooth, like a round shape, it will not align). On the other hand, everything else needs to be smooth, like a topography is - the plateaus are human-made cuts, with sharp edges, not natural like natural topography is). So in my thinking, with a subd, I would achieve this smoothness and sharpness edges at the same time.
This topic could tell more about what I’m looking for, as I said at the beginning of the this topic: How to create a smooth mesh plateau.
By the way, how did you achieve this result with mesh and nurbs? These are good results, and I could use them.