For continent scales you should definitely use procedural shaders (Power Fractal being the primary - but not only - one) and not heightfields. You can get non-global features by using masks, as Dune mentions above. Masks can be procedural (large-scale Power Fractals, as stated above), but you can also use Image Maps for example, so you could paint a rough continent shape in an image editor and use that as a mask for a Power Fractal to get the right continent shape, with procedural detail inside it. Taking that a step further you can then paint individual masks for areas where you want mountains, hills, and plains, then use different procedural shaders (e.g. Power Fractals) with different settings to create each terrain type and use the masks you painted to blend between them. You can also use the built-in Painted Shader for basic masking.
- Oshyan
