Ok, so this is what I have in mind, going from the whole "journey" of One Piece I think it represents the human progress in general, it is a journey where everything seems to get "scarier, bigger, more advanced, more complex" as the story goes on, more characters, more information as well, it is a like a world we are yet uncovering.
It can also be seen as an allegory on geography and the Great Geographical explorations, I mean we are clearly moving from East(Alabasta) to West(New World) as represented allegorically from the real life world.
Can you see some more comparisons and allegories in the manga as well?
OP always had a strong element of geography in it, which covers both technical aspects (e.g. log pole) and the actual geography. The grand line obviously represents the equator dividing the world into two halfs. Looking back at it, you might say that after the F.I arc Oda finally completed all possible directions in which the strawhats could possibly travel (up, down, left, right ).
I think that the reason Oda picked a line that can't be entered by a particular sea has a wonderful meaning: It could mean that no matter you're from, you're able to go to the top. Maybe I'm reading too much into that, but I like to think it this way.
im not sure if this is the right forum for this....but in every pirate map...the treasure looks like a big X.
1. the strawhats needs to go back to fishman island...(i dont think they can backtrack...so they need go around one more time? or there is another pathway?)
2. need to get back to laboon once again.
3. all blue is a sea that converge into one.
4. only guy who knows how to read poneglyph and hears the voice of all things will find one piece.
***strawhats ventured on almost every type of journey - sea, land, sky and underwater...only two things left, space (which im not sure since its a pirate world) and underworld (which is likely possible since its a pirate world.)
**** now, what im thinking is:
WHAT IF (a big IF) the reverse mountain (the VERY TOP) is the entrance to raftel???....and doesnt it look like that the reverse mountain, when you look at it on eagle's eye view...looks like a PIRATE MAP'S X?????
1. maybe they would enter a world under....like hell or another underwater passage. in order to reach a secret island and another secret route to fishman isle.
2. laboon is just on the other side.
3. reverse mountain converges ALL the 4 seas.
4. robin can read poneglyph and luffy hears the voice of all things...maybe if they reach the other side and gone back to reverse mountain...its a dead end. then luffy hears a voice to turn the ship upside down to find a secret passageway in the reverse mountain. (this would be much more likeable if they recruit a ship-coater----get why? turning the ship upside down)
You'll find quite interesting that you had the same idea and sometimes even the same words than mine from almost two years ago