Right now, I'm working on some methods for building roads on heightmap generated terrain. I start with a series of randomly located points, and I tesselate a curve connecting these points. From this curve, I build a quadstrip, then iterate the strip plunking down quads. (I made a modification to the float buffer class to provide functions for triangle rasterization; new version of Accidental to reflect the changes should be up some time soon.) The values rasterized by the quadstrip are elevation values. The result is something like this:
I can superimpose this road on generated terrain, then use a mask buffer to keep subsequent noise perturbations from affecting it too greatly, and the result is a smooth and sensical road through the wilderness. It's hard to demonstrate some of these techniques using only a limited 2D based engine.
At some point in the future, I may want to rebuild Accidental, or build an Accidental 2 and base it on something like the Golem3D basecode so I can demonstrate techniques involving heightmap stuff.