Stencil maps

Stencil maps (texture splatting)
Stencil maps for terrain, also referred to as texture splatting:
 * http://wiki.fifengine.de/images/8/8a/Mixing_grounds5.png
 * http://www.jenkz.org/articles/terraintexture.htm
 * http://en.wikipedia.org/wiki/Texture_splatting
 * http://www.gamedev.net/reference/articles/article2238.asp

Similar to texture splatting is the way Freecol handles terrain, would be probably worth asking around as an alternative to texture splatting method: http://www.freecol.org/ (on second thought, this method is only good if you want to keep borders between different grounds straight, PARPG would need more than this)