Thanks for those links!
I'm looking for something like that but which works at about the 1km "scale" i.e. a height_field that can represent a 2km square of land for placing models at 1 meter "resolution" on - basically places and scales you'd expect to find a village, town or castle. Options for flatness adjustable to "rockiness" would be good. For particularly steep fields the ability to edit for "terracing" and embankments/cuttings would also be fun!