Hi JTippetts and thanks for your reply i definitely got the point.. in fact, my very first problem is about the effective scale of the map compared to the "real" proportion with human/plants/etc...
I had the feeling that my object was oversized but i couldn't get HOW MUCH it was o/s... you explained it and cleared the point
And the second point was "why almost all the terrain editor have map range between 2k x 2k to 4k x 4k as max size"..
Now, just to hit the spot.. I have the border of all my lands (in spline form) + a grayscale heighmap... what's the best tool i can use?
ATM I'm working with Grome, World Builder and VNS (plus the UDK module for landscaping).. i'd like to keep the landscape modelig outside UDK to have a stand alone model to import in any engine i could ever use, but i don't know if it can be easier.. i have to say that WB and VNS are GREAT tools indeed.. it's hard for me to quit using them and use a less powerful tool (but i have to say, i don't really know the UDK capabilities in landscape modeling).
by now, i will resize my model.. and hope to post some WIP soon