Why would i need multiple UWorlds in my game?

I dont understand, why UE4 support multiple UWorlds?

As i understand UWorld is used as a global class for ENTIRE world? Why we need multiple ENTIRE worlds, how can it be?

One reason would be for multiple World Composition based worlds since all the logic for the World Composition is part of UWorld, so you cannot stream in a World Composition based world like you can levels, instead you have to change to a new UWorld. For example, my game has multiple worlds, somewhere in the 20’s at the moment, each of these exist as their own UWorld, then I have multiple interior cells you can travel to from these worlds, they exist as levels and can be streamed into these Worlds.

I guess it would be client, I am doing a single player game, no server, no networking. World Composition is for large worlds where it automatically controls the streaming in and out of sub levels (cells) as you walk around (and controls distant LOD). Where as level streaming has to be specially setup with either distance based volumes, or trigger volumes.

My game so far has twenty distinct worlds, and each have numerous interior streaming levels (So I am using a combination of World Composition for the exterior, and leaving streaming for the interior).

Your Client have 20 worlds? Or you talking about Server? I still dont understand, why Client would need World Composition. Because i can use Level Streaming, specially made for that purpose…

No. UWorld encompasses a World. Which when using World Composition will comprise of a number of sub levels (ULevel) for each cell of that world. If you require multiple worlds (Think different planets for example). Then you will have multiple maps set up with World Composition (each of these exist as a different UWorld when loaded) and each of these will have a number of sublevels (cells). You cannot level stream in a map that has World Composition ticked into another map that also has World Composition ticked, this is because they are seperate UWorld’s, they cannot exist together.

So, UWorld intended to be used as Cell of 2D Map for Outdoor Environment / Terrain? And Levels should be used for Indoor Rooms / Caves?

Ok, so new UWorld is used for different World Compositions?

Thats one purpose. There could be others that I am not aware of.