Vraciu,
I created a 10 layer project file in Paint.Net on a work space 4096x4096 so my land, water and bases were 1:1 to the terrain editor work space. The terrain editor work space is 4096x4096, 8-pixel=1mile. My project file has the land and ocean on one layer then I separated onto individual layers the 1mile or 10pixal diameter dots that equal bases, base numbers\ types and strats, GV spawns and PT spawns.
I was able to use the land\water layer to convert it into a 16 color grayscale file that I then converted into a heightmap file which I imported into the terrain editor and all of the land as 500ft level blanks, the 25,000ft barrer ring mountain range and water gaps was created in about 5 seconds. I converted those brown corners into a gradient so the corners touch the mountains at about 15k and run off to about 100ft in the corners. That mountain ring is how I end up with a hybrid terrain of 14x14 instead of 20x20.
No matter the size of terrain you create, the work space will be 4096x4096 8pixel = 1mile while you use the CBM map size to mask out what you are not using, say if you create a 2048x2048 10x10 sector terrain.
Here is a screen shot of the 4096x4096 base layer, feilds number\type and spawns enabled from the 10 layers I used. With this I was able to map out my base locations to exactly where they will be on my terrain based on the distance requirements for bases on a Melee arena terrain. Also knowing how far from each field my spawns will be, the arrows at the end of each yellow GV spawn line are exactly where they will be when I finally lay down GV spawns to bases. It's all in the pixles on a 4096x4096 work space.