One File Per Actor (OFPA)

In World Partition maps, each actor is saved as its own .uasset file under <Map>/__ExternalActors__/. The map itself is a tiny stub.

Why

• Merge-friendly — two artists editing different actors don't conflict in source control
• Streaming-friendly — load only the actors needed for a cell
• Editor scalability — open a 100k-actor world without loading all of it

File layout

<Project>/Content/Maps/MyWorld.umap                     # the tiny map stub
<Project>/Content/Maps/__ExternalActors__/MyWorld/
  0/B5/D9/2F3C-...-MyActor_01.uasset
  ...
<Project>/Content/Maps/__ExternalObjects__/MyWorld/
  0/B5/D9/2F3C-...-MyComponent.uasset

Filenames are content-addressed hashes — git-friendly, no rename conflicts.

Source control

VCS	Behavior
Git LFS	Each actor is a tiny binary file — fast clones
Perforce	Per-actor exclusive checkout — no more locking the entire map
Plastic	Item-level merge support

Reverting / debugging

The External Actor files can be diffed individually via the UE diff tool. The Levels window shows which actors are loaded (highlighted) vs unloaded (greyed).

Common pitfalls

• Submitting a map without the matching __ExternalActors__/ files breaks the build.
• Renaming a map: also rename the matching external actor folder.
• Non-WP maps: OFPA isn't used — actors live inside the .umap.

See also

• World Partition
• Data Layers