The problem with making bigger maps is details...The easiest method is Ridge-Valley-Ridge-Valley etc..... What this wont' allow much of is long long range sight lines..
It seems to me that this problem defeats the object of having a large map, with extended viewdistances.
A terrain can only be so interesting, it needs to be a pretty high res or it will look crude scaled up to a large map-and to make it interesting you need peaks a variation of relief. As you say ridges allow long viewing distance, which is what you want for a large tankmap but it kills performance, especially if overlooking areas of trees, buildings or other visual interest- yet you need these areas to break up the terrain.
The ridge/valley approach as you say i can see as the best approach, but this map would have to be pretty linear and long (unless you had atificial 'rice paddy' style ridges at angles too each other). You would end up with a series of setpieces, fine for bere but on a huge map it would be like a bizarre long obstacle course. This affect would appear even more artificial with long viewdistance because the ridges also have to be of a similar height to prevent overlooking too large a distance. (Though I appreciate you can place occluding planes in treelines on ridges)
I am of the understanding that there are only so many 'antiportals' it is advisable to use in a map- about a dozen maybe less? I gather theres a point at which their non rendering benifits are out weighed by their own demands on the engine?
Keeping a map interesting, semi-natural looking looking and running well it seems like you cant get away with a map much bigger than orel anyway.
As pointed out in Orel- even using mearly 2000m viewdistance (never mind longer) you can still just about plug away at the enemy spawn from the central heights area.
Huge tank map's clearly aren't impossible, but I doubt it would live up to the maker's vision to the extent a smaller map would.
It appears to me like a vicious circle when planning a ultra large map- tank or not, with the extended view distances there simply to tease.
BTW, I strongly agree with the opinion that these maps may only realy be suited to n. africa setting- after all when I've played around with huge maps in the editor they always look like the desert whether I like it or not!
Sorry for off topic discussion- quietus, I look forward to checking out your latest version when I have more time.