optimizing tilemapping? any ideas or links or whatever

[realMakc]

for tile map 100x100 and more, to be drawn by beginBitmapFill()/drawRect(), I made an optimization routine that combines tiles with same fill into larger rectangles to have less drawRect() calls. however, my algorithm is suboptimal, as you can see here; I would like any pointers for existing solutions and/or ideas, anyone. even appropriate search terms could help. thanks