First topic message reminder :The Blue SeaThe Blue Sea, which is where the bulk of the storyline takes place, consists of one large continent, one long chain of islands, and Four Seas that make up two larger oceans. The continent is called Red Line, the big chain of islands is called the Grand Line and the Four Seas are called North Blue, South Blue, East Blue and West Blue. The map below should be helpful to visualize that.
The Red LineThe Red Line is the one and only continent in the One Piece world. It circles the entire world from north to south. The Red Line seperates the two oceans into four smaller seas. One ocean makes the two seas East Blue and South Blue, the other one makes North Blue and West Blue.
The Four BluesAs explained above North Blue, South Blue, East Blue and West Blue make up the four seas of the world. Within each Blue, sea travel works as it does in the real world. You can sail to any destination you want with a regular compass or other navigational equipment. However getting from one Blue to one other is much more difficult as the four Blues are seperated from one another by geography. The Red Line divides the globe into Eastern and Western Hemispheres, while the Grand Line and Calm Belts divide it into Northern and Southern Hemispheres.
The Calm BeltA Calm Belt is a sea area that borders on each side of the Grand Line as the picture below shows.
These regions are constantly calm. Winds do not blow and sea currents do not flow within this region of the sea, hence the name Calm Belt. As a result, sailing through this area is difficult. However, an even larger reason to avoid the Calm Belt is because these areas are the nesting ground for Sea Kings of the largest variety. Even if a ship doesn´t require wind or currents to sail, it would still be in danger of being attacked by these creatures that can be the size of islands. These two reasons are why the chances of entering the Grand Line by this method are very slim.
The Grand LineThe Grand Line and the Red Line have one thing in common. Both circle the entire world. But unlike the Red Line, the Grand Line goes from east to west, thus functioning as an equator, and is the primary searoute in the entire world. The Grand Line isn´t a continent, but one big line of islands that come one after another. Since the Grand Line is surrounded by the Calm Belt on both sides, it isn´t easy to enter this route. The primary entrance to the Grand Line can be found at Reverse Mountain, which is shown in the picture below.
As the map shows, Reverse Mountain is one of the two points where Red Line and Grand Line meet each other. Reverse Mountain reaches into each of the four Blues. Each Blue has an entrance at the foot of the mountain. The entrance is a river that flows up the mountain thanks to the immensely strong flowing current. Since the currents are so strong that they can make rivers flow up instead of down the mountain, maneuvering under these conditions is very hard. And if a ship misses the entrance then it heads directly into the mountain and cruahes there. That´s why entering the Grand Line is a difficult task for most. However if a ship successfully entered the river then it practically entered the Grand Line already. The rivers from all four Blue´s flow to the top of the mountain and from there on there´s only one river that flows down again and that one takes the ships directly to the beginning of the Grand Line, which is the Cape of the Twin Lighthouses.
Once a ship has entered the Grand Line it enters a sealane with its own strong magnetic field, which diverges into seven smaller fields. The islands of the Grand Line each are so rich with minerals that they cause abnormal magnetic fields along the entire line, which makes the usage of a regular compasses impossible. To navigate safely through the Grand Line, the crew needs a Log Pose. A Log Pose is a special kind of compass that adapts the magnetic field of the next island. Below is an image that shows how this sort of navigation works.
After the Log Pose has adapted to the magnetic field of the next island, it will constanly point in it´s direction showing the crew the correct direction towards an island. After the crew has landed at the island the Log Pose takes some time to acquire the magnetic field of the next island and then everything starts all over again. Traveling through the Grand Line is thus step by step. There are different routes that can be taken to travel that way and this can only be done at the beginning of the Grand Line at the Cape of Twin Lighthouses.
From here on there´s seven routes that can be taken. Each one begins with an island and once a route is entered there´s no turning back and it has to be followed until the end. The image below shows how that works.
Click to to see large Image
Each of the seven routes follows the same step by step traveling rule. As it can be seen on the image further down the routes the Grand Line meets the Red Line for a second time, but as seen on the image the journey doesn´t end there. How exactly the routes cross the Red Line isn´t clear yet because the story didn´t get to that point yet. The routes themselves will sooner or later meet and join with each other until they all become one final route that ends at the last island of the Grand Line, Raftel. What waits there and how the Grand Line can be left from there on is yet to be revealed.
As explained, following the step by step rule with a Log Pose is an easy way to navigate the Grand Line. What makes travels on the Grand Line is the climatic conditions there. The many islands with their magnetic fields cause huge disturbances in the weather. On the direct route from one island to the other the weather can change from sunny to strom to snow to sunny again all pretty rapidly. Predicting the clima is impossible there and Hurricane´s can come up in a second and destroy entire fleets. This climatic disturbances are what makes the travels within the Grand Line dangerous. The only places where the weather is stabilized is within the magnetic field of the islands themselves.
There is also the possibility that the Grand Line can be exited and entered at or near the Holy Land of Mariejoa, but this has not yet been confirmed.
As a final note on the Grand Line, the region of that sealane between Mariejoa and Raftel (or that seperates North Blue and West Blue) is known as The New World. It appears to be home to some of the strongest pirate crews and is presumably more dangerous than the first half of the Grand Line.
The Sky OceanThe Sky Ocean is a place that is unknown to most people in the Blue Sea. The reason for that is that the Sky Ocean is entirely made of clouds, which from the Blue Sea doesn´t look like an ocean in which people live after all. The Sky Ocean clouds however are no normal clouds. There´s two kind of clouds up there, Sea Clouds and Island Clouds. Sea Clouds are just as water, which means that you can sail on it if you´re not to have to sink through it, whereas Island Clouds are dense enough to carry all kinds of things.
The reason why such clouds can exist explain itself through an extraordinary solidification process. The responsible element for this is Seastone which comes from the Blue Sea. It can be found in \"Pyrobloin\" which is a sulfur protein particle that gets transported into the sky through volcano eruptions. When it reacts with the vapor, the differences in density determine whether Sea or Island Cloud will be formed. The image blow should help to visualize it.
There´s different ways to get to the Sky Ocean from the Blue Sea. The only way that has been shown so far is the unorthodox and dangerous way in which the sailors have to to take a Knock Up Stream (soon to be explained more deeply). Not shown, but described is High West, which is the more typical method of reaching the White Sea. The Knock-Up Stream is reknowned as an all or nothing method; either the whole crew lives or the whole crew dies. Arriving by High West all but guarantees that some, but not all, of the crew will make the journey intact. It is not yet known why this is.
In the Sky Ocean there´s two known sea´s, the White Sea and the White White Sea.
The White SeaThis sea lies 7000 meters above the surface. It is the lower one of the two seas and lies between the Blue Sea and the White White Sea. To get to the White White sea from here one has to take the Milky Road road which is a manufactured river of sea clouds. The only known place where a Milky Road that leads to the upper sea can be found is Heaven´s Gate.
The White White Sea
The higher of the two known seas in the sky. It lies 10.000 meters above the surface of the Blue Sea. To get to the White Sea from here the same Milky Road as mentioned above can be taken. Whether or not there´s other Milky Roads that connect the White White Sea to the White Sea is not known so far.
To leave the Sky Ocean one has to go to Clouds end and take an Octopus Balloon there. The Octopus Ballon which grabs the ship that wants to get to the Blue Sea, blows itself up with hot air and slowly glides down.
Others:
The Four BluesJayaGoing MerryOmasturi Island~credits to the original uploader~