On the battleground, each unit has its own different way of calculating its movement on different terrain, making some kinds of terrain impassible to certain units or greatly decreasing the distance the unit can move.
|Water||Can't be passed|
The calculation of the how far a unit can move is done by using the movement of the certain unit to deduce the movement cost of the terrain the unit will pass through until the remain movement become not enough to go to any adjacent terrain. If a unit has a route of a unit contains mostly plains, it could move further. On the other hand, if a unit only has route that contains mostly swamp terrain, it just cannot move far away.