While the Four-Point Spell tells <PERSON> where North is, he also has other important pieces of information:
* the maze occupies the area of the Quidditch Pitch (an oval 500 feet long and a 180 feet wide)
* the goal is to reach the center of the maze
How does he use this information?
1. At the get-go <PERSON> knows the distance from his position to the cup (of course, the other champions know this too).
For example, if the champions enter the maze from South and the longer axis of the pitch runs N-S <PERSON> knows that the cup is 250 feet North (this is probably not the case, but bear with me).
1. Now, <PERSON> need to keep track of the distance he travels in the North-South direction and in the East-West direction:
For every step he is forced to take East or West, he knows he will have to later take a step in the opposite direction.
Moving North decreases his distance from the cup; should he move North more than 250 feet, he would have to start moving South when possible.
1. 300
Every time he meets a fork, he can make a decision according to the cup's relative position (i.e. choosing the path that seems to go in the direction of the cup, or avoiding the one going in a completely different direction).
In order to have an (approximate) idea of the length he is walking, he can either count his steps or look at the end of the "segment" and estimate that distance (being a Quidditch player, he is probably quite good at it).
However, knowing the cup is currently 50 feet West and 20 feet South would have no use if he didn't know anymore where West and South are due to all the turns he took.
Vice versa, knowing where North is would not give him a clue if he didn't know the direction of the cup. So, the spell is a helpful tool, but it is not enough to guide <PERSON> effortlessly to the cup (otherwise, it would probably be considered cheating).
Bottom line:
The Four-Point Spell tells <PERSON> in which direction he is moving, so that he can correctly update his mental record of the cup's relative position. 300