it is crazy, but as long as its broken up, each item of variation or difference will build up, so its no different to a normal track really just the same stuff at different scale. I take care of the bulk stuff and itll take of itself really. and Scotland theme is wide and baron mostly with little pockets of habitation or amenities etc.
I'm carefull to consider lod distances that will hopefully draw these little area out of memory when your not in them etc. for example I will apply lod to any barrier and when 500 or more away from it ill undrawn it from the scene, and little areas will always more than 500 m from anything else. and the little area might have lod figures to it undraws at over 500 m distance. and each little built up area will be at least 500 m distance from any other little area etc and built behind base scenery and generally unviewable from most areas or obfuscated by other objects with higher lod figures etc. etc. and we will just go on and on till we decide its done. being a massive areas has its advantages theoretically in terms of all this unloading. its how GTA engine works. they use 8 lod models, whilst I'm not going to invoke a lower quality model, I'm happy to turn shit off completely.
experimenting with large side details, I ripped an image from google street view and made this. not entirely happy with it, its just the wrong art. but something like this can work quite well in certain areas. of course here ive blown the scale up which was a bad idea pixel space wise."but" as a multilayer controller diffuse and mask from it could be nice.