The New World is the second half of the Grand Line. It stretches from Mary Geoise to the other side of Reverse Mountain. The second half of the Grand Line is a whole “new world” of adventures beyond anything that one might face in the first half, it is such an abhorrent challenge that the first half of the Grand Line is referred to as "Paradise" when comparing it to the second half. According to former Warlord, Gecko Moria, one will lose everything one cherishes in the New World, something he personally experienced. He also claimed that one shall face what he calls "The Ultimate Nightmare" there, indicating it is a very dangerous place for even the most powerful and talented pirates like himself.
While the first half of the Grand Line possesses highly volatile and unpredictable weather conditions, the New World is even more chaotic. While certain islands are relatively simple in terms of weather and climate, such as the snowy Yukiryu Island and the rainy island the Kid Pirates were on, other portions of the ocean defy the very laws of physics and nature themselves. Examples include the lightning rain of Raijin Island, the Firetank Pirates being drawn toward a giant black sphere floating in the sky in the middle of the sea, and the On Air Pirates running on air.
Islands in the New World experience changes in their magnetic waves, which makes a special New World Log Pose necessary so as not to get lost. Instability of an islands magnetic field can often be caused by abnormalities on the island. As a result of the unstable magnetic waves, the Log Pose needle pointing toward that island will jiggle, the more erratic the needles movement, the greater the instability of the magnetism. There are no guarantees, but the rule of thumb is that the erratic movement of a needle means that there is likely something dangerous on the island it’s pointing to.
Somewhere in the New World is an island with a special shop where Vivre Cards are manufactured. The Marine BaseG-5 also resides here, and according to Aokiji, it is full of problems. As is later demonstrated, the Marines of this base are wild and tend not to follow their orders.
The unfixed, seafaring Germa Kingdom (Sanji's home country) is currently located in the New World. However, as the kingdom originated in North Blue, its rulers must possess some method of transporting dozens of ships across the Calm Belt.
This is a concept unique to the New World. Due to the presence of four powerful pirate crews under the reign of the Four Emperors who reside in the New World, all of them possess many territories widespread across its sea. These territories are used as the respective Emperor sees fit; for example, Charlotte Linlin has the territories she occupies make various sweets for her as tributes, with the citizens free to live as they please as long as they deliver on time; whilst Kaidou converted one of his into a weapon-making factory and enslaved all able-bodied citizens to work there. While this may seem like a dictatorship of a foreign power, the Emperor's claim over an island can actually protect the citizens from other pirates, though the situation varies greatly between the Emperor guardian. This is exemplified when Edward Newgate declared Fish-Man Island as his turf, as it caused the constant kidnappings of its citizens by other pirates to cease completely, even though the island was already affiliated with the World Government.
However, not all the islands in the New World belong to the Four Emperors. Some are under the protection of the Marines; others may have their own powerful military force like the Wano Country possesses (though it was later conquered by Kaidou); a few might be isolated or require special methods to reach it, like Zou; and certain islands may be under the jurisdiction of powerful or influential individuals like the Seven Warlords of the Sea.
An Island with harsh snowstorms that the Red Hair Pirates stayed. This is where Portgas D. Ace led his crew as soon as they entered the New World so Ace could show his gratitude toward Shanks for helping Luffy. During Ace's visit to the island, the storm was somewhat calmed.
A foggy island. It has a vast pine forest and a mountain range.
An island the Whitebeard Pirates used for supply. Ace waited there for Whitebeard to come but was encountered by Jinbe, and the two fight. After a long fight, both fighters collapsed just before the Whitebeard Pirates arrived. Ace then protected his crew before being defeated by Whitebeard and offered to join the Emperor's crew. During Ace's visit to the island, the fog was somewhat cleared.
The New World is also the primary geographical setting for the network known as the Underworld, an underground network of black-market connections and illicit dealings which are beyond the World Government's control. Underworld activities, including weapons trading and the manufacture of SMILEs, occur in various islands throughout the New World, most prominently Punk Hazard and Dressrosa.