Multiple Terrain Textures? Please Help

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I'm really not sure how to make multiple terrain textures. For example, If I were making a coaster on an Island, I don't know how to make grass and sand in the same terratexture.

For a visual example:

RiscIt's "Alice's Day Dream"



RiscIt's "Crater Lake"



Thrill's "High Voltage"



I just want to know how to do this "smoothly." As a guess would it involve the Old Terraformer?

The only way I know how is to set a different texture for a certain height, then lower or raise certain parts a little. There may be a much simpler way though.

I guess they know the track plan and they just use there preferred image editor. then they play around with the repeat settings till it is right.

^ The Repeat Settings would then be set to 1 because if it's repeated, the secondary terrain texture would be repeated.