Or if you are not doing a specific location on planet earth, you can use known geological characteristics. I created an 18 sector diameter super volcano with a 26,000ft unbroken caldera wall. Then placed 9 islands in it as the remnants of the primary cooled magma. Then I scarred the islands with secondary and tertiary up upheavals and erosion edifices. Including runoff fjords for a continuous 4000 miles. Just think like water and cut and paint everything from the top of the hill down.
The 16 clutter tiles are very limiting to the granularity at the ground level you are able to really duplicate real world region topo maps. In FSO and special events we fly at nose bleed altitudes with converted topo maps of WW2 historic regions work. If someone wanted to do a custom terrain of Bastogne right down to the buildings and street layout from 1944 photos, they would be screwed.
The AH3 clutter tiles give us the ability to create the illusion of civilization which if you look at photos of England and the continent, airfields were surrounded with farm feilds, cities, towns and villages. And the village tiles make very good GV combat zones and spawns.
Here are some secondary geo features in my super volcano caldera. Hitech suggested I convert all of the exposed rock from a dull green stone tile to that very textured white stone. This is another drawback in the terrain editor for the euroterr set. No brown\gray textured rock. This is a snow covered or dolomite exposed rock tile. Europe has granite and basalt mountains also.
Some of the level landscape painting gets it's random large flows from the fact when I cut the elevations and smoothed them there were 25-100ft elevation irregularities from my mouse swipes. So using the tool that lets you specify painting areas with a tile, based on two elevation points, I got some nice natural flow irregularities that helped later creating all of the civilization. Then the rest was finger painting randomly since nature is a bit random except where water is concerned. The size of the polygons the terrain is created with will limit what you can really do at ground level along with how the tiles visually interface with each other for the sensibility's of the Gvers stuck out in the bushes. Just remember, Hitech's panther can climb forever up a 70 degree cliff face.