Flow maps are also used for AI pathfiding. Hybrid solution (lol "Hybrid") XD is to use both A* and flow map. Flow map generates a "derivate" of the map obstacles and terrain cost. a* search is similiar to a ray of light. It starts for a cell, and then go to another cell (or point of a grid). big derivate values "reflects" the search ray to a more suitable place for find paths. The only hard thing is to compute correct values for flow map. After that search time is reduced. Flow map also works well when many units need to move and avoid obstacles.