well, i never really tried making tile based game before, i used to make terrain using heightmap (perfectionistic; hate tiling patterns; err big mistake! :o ) but i think i should revisit my hindsight on a piece of good idea. anyway, what i hope to achieve is similiar to what was done with civ4, a tile based map drawn in 3d. i am looking to continuing using bitmap to store the data; they present terrain feature instead of height now. i need some clue on what options are available to read those information and merge them into a seemless terrain. i could tile the meshes together but i am new to making seemless tiling (hoping to find some existing ways to join the mesh). i am also exploring tiling technique as a means of removing Hidden Surfaces (unload tile that is too far away or unrelated to the current mission) thx for any help! :)

You're talking about the Dungeon Siege engine. The terrain is comprised of rectangular sections of geometry. They're built in 3ds max and converted to a format the game can use. They're placed and transformed in the Siege editor. The entire world is continuous; loading/releasing of geometry and textures is handled by the engine. Technically, DS is a true 3-D engine, but most of it looks and feels 2-D.

Outcast uses a similar 2-D approach but with voxels. I can't remember where I found them a long time ago, but there were some JPEG maps for all six regions in Outcast that demonstrated this tiling approach extremely well. Maybe you can google for them (be sure to add "-jedi" or you'll get a billion hits for Jedi Outcast).

Maybe looking at these games will give you ideas.