I think all this is true for the US...for remote countries the data may not be so easily available.

I'm thinking that for a small piece of land without too many contours, a more "low-tech" approach may also work: trace the contours in MoI from a background image and use loft or network. It should be possible to get a decent result like that.

Michael, is there any possibility to convert a polyline to a nurbs curve?