Remember that God hasn't told anyone how they were getting across the river. Just like at the Red Sea (and just like Abraham hundreds of years before), God simply told His people where to go and to trust Him with the details.

God was not planning on using house-to-house warfare to conquer the city. He was going to bring the walls down in one fell swoop. And yet, God honored the spies' arrangement and didn't destroy Rahab's family in their house in the wall! Rahab could trust God, even in things she didn't understand and couldn't comprehend. We can also trust God, even when we don't know what His plan is.

Anyway, the real point of all of this is not the maps, it's the promise from God -- God will be with Joshua just as He was with Moses, and Joshua will succeed in everything he does because God will give him success.