There have been a couple of tutorials on Height Field Scatter for terrains. This is for those of you still confused. It looks at the different types of scattering available, how to use variations, and instancing. It creates a wooded landscape with clearings and buildings.
It is worth looking at the video descriptions and comments as they often contain a breakdown of what is covered in each video, together with any errors or additional explanation.
All videos HD and best viewed full screen. All can be downloaded (see the individual video pages). Download versions are encoded at much higher quality than the Vimeo versions.