Well, the way a terrain is done in blitz is via a heightmap. Basically a square image (2x2,4x4,8x8,16x16....256x256,512x512..etc) i think it has to be square and a power of 2. Now the way it works is a pure white pixel is the highest value for height, whereas a black pixel is the lowest value for height.
And any grey-ish pixels are inbetween. So it depends on the brightness of a pixel. If you look in the samples of blitz3d and find one that uses a terrain, look in the media folder where all the graphics are, and you'll see what a heightmap looks like :)
As regards to adding hedges, they have to be added manually, but there are some blitz world builders out there that will make it easier for you :)
And any grey-ish pixels are inbetween. So it depends on the brightness of a pixel. If you look in the samples of blitz3d and find one that uses a terrain, look in the media folder where all the graphics are, and you'll see what a heightmap looks like :)
As regards to adding hedges, they have to be added manually, but there are some blitz world builders out there that will make it easier for you :)