not to sound stupid.. but couldn't you just generate two landscapes? one for the bottom, one for the top? *shrug*

OHHHH I get it. sorry

I don't know nothing about algoritams for terrain creation... so here is an idea.
If you can, how about you additionally generate some round type random irregular shapes on map and then substract them from original terrain. That way you can get caves, wholes in terrain or whatever... only problem is doing substraction.

wow, thanks  i have just found a good tutorial on metaballs, i'll give it a try tonight

well obviusly not since those ice-creams have horizontal pedestal that sticks out so they are computer generated.

I'm pretty sure the game advertised with "with over 4 billion maps!"

So it must have had a seed-based mapgenerator.

One way to do these things would be to define the boundary between ground and non-ground as a contour curve of some function f(x,y), where the values of f could be randomly generated according to - for example - a diamond-square algorithm. Of course this will treat the x and y axes equally, which might not be desirable when doing a sideways-viewed game. This method would require a grid, but one could interpolate to achieve smooth boundaries.

Of course lots of information is lost if you just use a contour. I'm sure there are more elegant ways to do this.