Creating Realistic Terrains

Hi, I'm just wondering if it's possible to make realistic terrain, in terms of the shape of it and the textures.

Examples

Red Dead Redemption GTA 4 (Land Areas/Offroad) Call of Juarez

Would you need to use a program such as World Machine 2 and Terragen or does everyone use Unity's terrain creator and is it the most decent thing to go for.

Thanks for reading

Do you mean realistic as you say only regarding the shape of it and textures, or are you asking about the size aswell? I don’t know about size but shape and textures are fully possible I suppose.

I myself use the Unity’s terrain creator and also make some 3d models for details and complex areas.

If you want more control over the terrain I suppose you could make the entire terrain in a 3d app cut it into parts and put together in unity.