Despite having memorised the best map of Westeros he could find, navigation turned out to be harder than he imagined. It often snowed, the sky was almost always covered by clouds, and the sun could scarcely be seen. Most landmarks in the North were quite indistinguishable, especially when covered in snow. One would simply see an endless white blanket in every direction, and there was not much guarantee that the map was fully accurate, or even if it was that nothing had changed since it was drawn.