44 "lands" crammed into a single world. That's Battleworld, the setting of Marvel's universe-ending-and-rebirthing mega-event, Secret Wars.
Kicking off in May 2015, Secret Wars is set entirely on this mysterious Battleworld, with territorial battles and mysteries (such as who created Battleworld and why) expected to comprise the main storyline. Some of Battleworld's lands are actual alternate universes that have been featured in Marvel stories going back decades, like the Ultimate Universe or the future Earth from the "Old Man Logan" storyline. Others are entirely new universes based on past Marvel events, where those conflicts either never ended or ended differently than we remember them. Civil War and House of M are just a few examples.
Here's a list of all 44 lands that make up Battleworld, along with what we know about them.
Notice that similar lands are grouped together. For example, #1 and #2 are both expected to be Hulk-related, so they share a border, while the several Spider-Man-related lands are clustered in a single region.
Teaser imagery connects Greenland to the Hulk, and the "Planet Hulk" storyline in particular.
Earth-9200. A future, post-apocalyptic Earth from a storyline called "Future Imperfect." Here, an old and embittered Hulk became known as "Maestro" and ruled with an iron (er, green) fist.
3. Domain of Apocalypse
Earth-295. The "Age of Apocalypse" universe was created by Professor X's son. Xavier is dead, Magneto leads the X-Men, there are no non-mutant superheroes, and an uber-baddie named Apocalypse wages war on homo sapiens.
Earth-9105. Of all the possibilities, it's unlikely anybody saw this one coming. An old New Warriors storyline called "Forever Yesterday" introduced this world where Moses never lead the Israelites out of Egypt, causing Egypt to become the major world power.
Related to Iron Man's "Armor Wars" storyline, based on artwork. Could be a world where the Armor Wars are still raging, with Tony Stark battling armies built on his own stolen technology. Or it could be set on Earth-89120, based on the story told in the one-shot What If Iron Man Lost the Armor Wars?
Like its miniseries namesake, it's safe to assume that this is a version of Manhattan where the entire population gains Spider-Man's abilities — but were reverted to normal. Spiderverse could also play a part in this somehow.
8. The Regency
This one's a real head-scratcher. Teaser art has linked it to the despised "One More Day" story, where Peter Parker and Mary Jane's marriage was erased by Mephisto, which means this could be a world where those events never took place and Peter and MJ are still married. One image featuring Peter, MJ, and their daughter suggests a connection to Earth-982, aka MC2, where a teenage May Parker becomes better known as Spider-Girl.
9. King James' England
Earth-311. This has to be a reference to the Victorian world from Neil Gaiman's Marvel 1602.
It's anybody's guess what this refers to, but the only "Weirdworld" that already exists in Marvel continuity is a very obscure, Tolkien-esque fantasy world created by Jack Kirby in the 1970s.
The mystical eternal city where Iron Fist gained his powers and tends to still visit often. Shang Chi is also connected to K'un-Lun.
Unknown, but this could be a world where Avengers vs. X-Men resulted in the X-Men winning. Meaning there are "no more Avengers."
13. New Mars
When writer Jonathan Hickman took over Avengers in 2013, his first story arc featured baddies Ex Nihilo and Abyss, who were seemingly terraforming Mars. This likely has something to do with that.
15. Higher Avalon
This is probably Otherworld, the parallel British realm where King Arthur still rules over Camelot. The Captain Britain Corps are headquartered here as well.
Obviously spider-related, this may have something to do with Spiderverse, or maybe the Spider Society seen in Amazing Spider-Man and Araña.
Whatever this one is, you can bet it's going to be weird. Could it be the world of the reviled comic miniseries of the same name? Seems unlikely. Preview artwork suggests it may be a parody land related to the work of Skottie Young.
18. The Eye of Agamotto
Connected to Doctor Strange, but how, exactly, is unknown. Perhaps it's a physical manifestation of Strange's oft-visited astral plane.
The island of Manhattan, the most familiar location in Marvel Comics, is present on Battleworld, but it's divided into four separate realms:
Home of the Inhumans.
20b. Marvel 616
This is the Marvel Universe as we know it, the "main" Marvel U where most of the current superheroes live and engage in daily heroics. The way they do.
20c. Marvel 1610
The Ultimate Universe, which is expected to bite the dust by the end of Secret Wars, merging its best elements (namely: Miles Morales) with the 616.
20d. Monster Metropolis
First seen in Punisher's "Frankencastle" storyline, Monster Metropolis is a realm beneath New York City inhabited by horrific monsters.
21. The City
This one's a mystery, but it could be a reference to Hickman's run on Ultimate Comics: The Ultimates, in which Reed Richards created an enclosed environment called "the City" where time was accelerated to allow for faster evolution.
22. The Warzone
Based on Marvel's preview artwork, the Warzone is the Civil War world. Which means it's a universe where Civil War is still happening. (If it were over, having a different outcome, it probably wouldn't still be known as a "warzone.")
23. New Quack City
A clear reference to Duckworld, aka Earth-791021. Possibly just a city on Duckworld or could be an amalgamation of the whole planet.
24. The Far East
Unknown, but could be Earth-2301, the Marvel Mangaverse.
25. Valley of Flame
Earth-78411. Homeworld of Devil Dinosaur.
26. The Hydra Empire
Its specific origins are unknown (there are several candidates), but this is undoubtedly a world where Hydra reigns supreme.
Earth-928, home of the future heroes and villains from the year 2099.
28. Hala Field
Hala is the homeworld of alien race the Kree, so obviously there's a connection there. The curious part is that Marvel is advertising Hala Field as having a connection to the current Captain Marvel -- Carol Danvers, a human. Hmm.
29. The Monarchy of M
A world where the House of M reality created by Scarlet Witch, where mutants dominate society, was never reverted to normal.
30. Sentinel Territories
Earth-811. In the future timeline where "Days of Future Past" took place, the Sentinel Territories are what used to be the U.S.A., a land where autonomous Sentinel robots have taken over, subjugated humanity and all but wiped out mutants. Curiously, the preview art changes the title to "Years of Future Past."
31. The Wastelands
The dusty post-apocalyptic future world where "Old Man Logan" took place, and almost all of the heroes are dead — murdered by Wolverine himself (but it wasn't his fault).
Unknown, but probably related to the X-Men's Utopia.
Tied to a promo image titled X-Men '92, the artwork features the X-Men as they appeared in the X-Men TV cartoon that debuted in (you guessed it) 1992. Sounds like it's a comic world that's based on a cartoon based on a comic world.
Unknown. Maybe a new version of Arcade's Murderworld?
Rumors suggest this may be the world of Marvel's old Shadowline imprint, a separate superhero universe created for "mature readers."
36. Bar Sinister
Aside from probably having something to do with X-Men villain Sinister, nothing is known about this land.
Marvel's version of Hell. Largely associated with the X-Men via Colossus' little sister Magik.
38. The Deadlands
Earth-2149. This is the world where Marvel Zombies takes place. You can bet that those undead nasties are going to hungrrrrr for all those delicious people across the rest of Battleworld.
The "perfected" Earth from "Age of Ultron," where evil android Ultron has taken over the world and imposed his totalitarian idea of order upon the populace. Based on the preview artwork, it looks like Perfection will be going to war with its neighbor, the zombie-infested Deadlands.
40. New Xander
Xandar is the home of the Nova Corps, and Marvel's promo images have tied this land into Infinity Gauntlet, though the planet was destroyed a few years back. That explains the "New" part, but why Marvel.com is calling it "Xander" instead of "Xandar" is unknown. (And perhaps just a typo.)
41. The Wall
Whatever this is, it stretches around the entire horizontal axis of the lower part of Battleworld, separating some of the more villainous regions from the rest. Most importantly, zombie home the Deadlands is located below the Wall. Very likely the Wall isn't a "land" related to any alternate universe at all, but is instead exactly what it sounds like.
* Three lands are still unaccounted for: #6, #14 and #19. But there's a huge number of locations or events that these three could be based on. Some possibilities: Asgard, the Supremeverse (of Squadron Supreme), Earth X, New Universe, or maybe a world where Secret Invasion never ended.