Talk:Road/@comment-26020061-20150203210937/@comment-25565811-20150203213628

They were generated by mathematical functions. These special functions are used to generate smooth curves which connect the points you want them to connect. You can also select in which direction the curve passes each point.

The calculation is quite complicated (I forgot most about it), the result is not. The modellers for new curved surfaces (e. g. the outer shape of a car) use these curves (or rather surfaces in that case, which works quite similar) a lot to invent things that do not (yet) exist.