I don’t know that terrain plays that much of a part in WAN design. I mean, unless you are the carrier and you are designing the long haul runs around a mountain, most network people never even think about this.
If you asked me today, what network topology to choose, I would first choose a protocol/service from a carrier – like MPLS, and then that would allow me a fully meshed network through their service. it would seem like a point to point link from me to them but I would, in turn, get full connectivitty to all sites, like a “cloud” or like the Internet.
Today, all enterprise networks are packet switching networks and there are still many point to point links in use for certain purposes.
No offense but this question sounds like one of those impractical text book questions that isn’t really connected to the “real world”.
I hope that helps.