Grand Line

The Grand Line (偉大なる航路 [グランドライン], Idai Naru Kōro [Gurando Rain], literally translated as Great Sea Route) is an ocean where much of the story takes place in the manga and anime of One Piece.

The Grand Line is the ocean current that follows an imaginary line that runs from north-west to south-east across the middle of the world and perpendicular to the Red Line. The Red Line is a vast continent that circles the globe from north-east to south-west. These two lines divide the two oceans of the world into four seas or Blues: North Blue, East Blue, West Blue, and South Blue. This stretch of ocean is said to be the most dangerous place in the world, and is sometimes referred to as the Pirates' Graveyard because of this reputation. Most believe that it is impossible to safely leave the Grand Line save at its beginning and end; however, the World Government regularly sends ships across the Calm Belts by coating their hulls with Seastone - this renders them invisible to the Sea Kings. The Grand Line is similar to the equator.

Calm Belt
To the north and south of the Grand Line are strips of ocean known as the "Calm Belts". The true entrance to Grand Line is usually marred by storms; the waters of the Calm Belts remain static year round, and there are virtually no winds or waves (this makes it difficult to cross without propulsion). Extremely large sea monsters called Sea Kings live in the Calm Belts; in fact, the monsters found in the Calm Belts are the largest shown thus far in all of One Piece. The combination of no currents, no wind, and the presence of the Sea Kings makes these belts perfect barriers to any traveler trying to directly go into the Grand Line.

Without using seastone-lined ships (which are concealed from the Sea kings to a certain degree) and some propulsion, the Grand Line can only be accessed at two points on the Red Line: Reverse Mountain and the Holy Land of Mariejois. The first is where the four major currents of the Blues merge together to form the Grand Line, while the second is the site of the World Government.

Halves
The Grand Line is divided by the Red Line into two halves. The first half, stretching from Reverse Mountain to the polar opposite point of the Red Line, is known as "Paradise". The second half, which starts beyond the second Red Line point to the backside of Reverse Mountain, is known as the "New World".

Paradise
The first half of the Grand Line is known as Paradise especially to those who have been to the New World. While the Grand Line is a dangerous place, the first half is known as such in comparison to the more terrifying dangers present in the New World.

New World
The New World is the second half of the Grand Line. This half has not been fully explored, except by the Pirate King, Gol D. Roger, himself. This area is also where the Yonkou reign.

Climate
The weather is unusual on the Grand Line. The currents and weather are extremely volatile, as they can change in an instant; this includes water spouts, storms, blizzards, and other such things. Islands and the surrounding waters are the only areas where weather and currents are stabilized in a predictable manner. The reason for this is that islands on the Grand Line fall into four basic categories: Winter, Spring, Summer, and Fall. These types of islands each have four seasons of their own, giving the Grand Line a total of 16 different seasons. There is also a cyclone that seems to appear quickly. Although being remarked as unpredictable, Nami was able to sense it coming even in a fevered state.

Navigation
Normal compasses do not work on the Grand Line because of the nature of its magnetic fields. In order to navigate the Grand Line, a special compass called a 'Log Pose' must be used. The Log Pose works by locking on to one island's magnetic field and then locking on to another island's magnetic field. The Log Pose can do this for a total of seven different routes that diverge from Reverse Mountain and travel east before merging again to the last island, Raftel. The time for a pose to set depends on the island. One island may take from a few hours to a few days to set to the next island, while another can take a year to set. This process can be bypassed by obtaining an 'Eternal Pose'. This version of the Log Pose is permanently set to a specific island and can never change. This makes it easier for a crew to get to a specific island rather than going through a trail of islands.

Paradise

 * Reverse Mountain
 * Cactus Island (Log change: less than a day)
 * Whiskey Peak
 * Little Garden (Prehistoric Island. Log change: 1 year)
 * Elbaf
 * Holliday Island
 * Drum Island (Type: Winter Island)
 * Bighorn
 * Drum Rockies (a group of tall tower-like mountains)
 * Robelle
 * Arabasta (Originally called "Sandy Island"; type: Summer Island):
 * Rainbase
 * Yuba
 * Erumalu
 * Nanohana
 * Katorea
 * Spiders Cafe
 * Alubarna
 * Jaya (Type: Spring island, Log change: 4 days)
 * Mock Town
 * Skypiea
 * White Sea
 * White-White Sea
 * Angel Island
 * Upper Yard
 * Milky Road
 * Long Ring Long Land
 * Sea Train Zone
 * Water 7 (Log change: 7 days)
 * Enies Lobby
 * San Faldo
 * Pucci
 * St. Poplar
 * Baltigo
 * The Florian Triangle Area
 * Sabaody Archipelago
 * Tarai Current
 * G-1
 * Mariejois
 * Fishman Island
 * Karakuri
 * Momoiro Island
 * Boin Archipelago
 * Namakura Island.
 * Kuraigana Island
 * Merveille

New World

 * Shanks' Jungle Island
 * Raftel
 * Yukiryuu Island
 * Wano Country
 * Foodvalten
 * Edd War
 * G-5 Marine Base
 * Marineford

Trivia

 * Most places in the Grand Line are known in the other oceans through the book "Brag Men", but are considered fairy tales to those who have never been there.