I've always had severe problems with fractal terrain generators. I've looked at a lot of maps, and the terrain they generate just don't look real to me.

Problem 1: Distribution

If you were to diagram the distribution of points in the standard fractal generator, you would likely find it follows a standard distribution curve. Unfortunately, terrain doesn't do that on Earth. While I don't know what it looks like in reality, it probably follows something like a concave curve coming to a point instead of the smooth convex curve of the standard distribution.

However, it occurs to me that you might be able to fake the proper distribution by applying a geometric function. Does anyone know how to "flatten" a grayscale image and then apply pixel^x function to it in a program like GIMP?

Problem 2: Fractal Lines

The fractal algorithms used for terrain aren't biased in terms of direction. Unfortunately, again, the real world doesn't work that way. The action of tectonic plates create fractal lines not radiating fractals. What fractal generator has ever created a structure like the Japanese islands?

Is there a fractal generator for producing marble veins or crumpled-paper-like patterns?

Problem 3: Erosion

Erosion makes hard edges smooth. It can also fill basins and cut canyons.

Is there some way to represent erosion on a fractal map?