I only mentioned LOD because you said "I assume that they try to interpolate 1 poly into many small poly for smoothment". For this type of overhead view, you don't need to bother with LOD, since the terrain is all roughly the same distance from the camera.
"Soft filtering and noise for terrain lighting" -> I don't know what this is either. It just sounds like a bunch of buzzwords put in a sentence. It's difficult to say without more context. Do you have a link?
Yes , here is the link. Thanks for the answer. http://www.ageofempires.com/age2.html (search for noise)
I'm working with the heightMap solution now. Divide each tile into smaller one. assign the height of it. Render all of them together.
Trying use this : http://www.nfostergames.com/lessons/TerrainSmoothing.htm for smoothing. But the result is quite different from what I expected. It only smooth surround the elevated tile. Not the tiles surround it.
Maybe I understand the algorith wrong, or fail to apply!