Forge World is a multiplayer map from the upcoming game Halo: Reach, set in a Halo Array. It first appeared in a Red versus Blue PSA (public service announcement) that was made in celebration of Bungie Day 2010. It originally appeared as solely a remake of the iconic fan favorite Halo: Combat Evolved map Blood Gulch, but that was revealed in the Forge World ViDoc on July 22nd 2010 to merely be a portion of the largest map in the Halo series.
Forge World allows players to create entire maps in a number of different settings within the main map. It was originally designed to be consisted of five maps but due to time it was dropped, and the idea of a whole big map was originated. The players can see the boundary of the other maps in the current map without exiting to another, preventing chaos while playing.
Forge World has five different unique settings on which maps can be created or played on, with most sharing a common theme of Forerunner technology on a luscious green backdrop. Originally these were five separate maps, but were merged into one when Forge World was conceived.
The first is the Canyon, which is modeled as an almost exact replica of Halo: Combat Evolved's Blood Gulch. All of the original caves, nooks and crannies all return. The only main difference between the two is the environment; with the new incarceration being much greener then the previous.
The second is the Coliseum, an enclosed interior similar to the Crypt found on Sandbox. It can be accessed through a pocket on the side of the cliff, and is the only portion of Forge World that's entirely indoors.
The third portion of the map is the Island. The Island a symmetrical body of land surrounded by water in the shape of a "U". There is a center rock with a small tunnel that cuts through it, much like Sidewinder or Avalanche.
The fourth is known as Montana, and its been described as a "very small, outdoor pocket." It's located on the edge of a cliff, and like the Coliseum, is similar in size to the crypt.
The final location is called Alaska, and it is a very tall, corkscrew shaped rock that was actually based off of Halo 2's Ascension.
Bungie is actually shipping maps that they've created via Forge World on the Halo: Reach disc, with these maps appearing alongside others in Matchmaking and in the shipped map roster. The first is Forge World itself, the empty canvas of the map.
The second is Hemorrhage, the Blood Gulch remake built within the confines of the Canyon.
The third is Pinnacle, an Ascension remake forged atop Alaska.
The fourth is Paradiso, a new map on the Island which looks to support large scale battles.
The fifth is The Cage, a "spiritual successor" of Halo 2's Lockout and the Halo 3 maps Blackout and Guardian.
The sixth is Asylum, a remake of Halo 2's Sanctuary.
Also included is a new Grifball map appropriately titled Grifball Court that likely takes place in either Montana or the Coliseum