User blog comment:Kaido King of the Beasts/Chapter 818: Stepping Stones to One Piece/@comment-3177945-20160303224020/@comment-181.230.122.206-20160304014706

The only reason why maps can't be used on the Grand Line is because you can't use compasses. When you enter the Grand Line you lose your directions, you're no longer able to know where North, South, West or East are, so you use the Log Pose to go to the next island.

Except for Islands like Zou that are constantly moving, if you drew a map, and if you know which direction you need to take, there wouldn't be any problem.

So, if this is true, Nami would need to draw a map of the entire world, fulfilling her dream, and with that she will take Luffy to Raftel.

Maybe every Straw Hat will fulfil their own dream before Luffy finally arrives at Raftel