Scene File Size

I spent time searching for answers, but did not find anything that matches my exact question.

I am curious why the .unity scene files are so large. In my case they are two to five MB each. here is how I have the project structured.
Objects - basic prefabs for props, vehicles, spawn points, vehicle paths…
Spawn Pool - A single prefab with instances of props and vehicles.
Sections - Nine separate modules containing:
Building / street mesh
Spawn points
Triggers to activate the spawn points
Collision, simple box colliders configured to fit around the building / street.
Vehicle Paths, a prefab of vehicle path nodes and spawn points.

Level - One spawn pool, instances of the sections (average of 16 per level), a gameplay prefab that has the character, and a few other small prefabs needed for gameplay.

Asset Sizes
Textures 3.5 mb 5.2%
Meshes 342.3 kb 0.5%
Animations 106.9 kb 0.2%
Sounds 9.8 mb 14.5% (Have not focused on proper compression yet)
Shaders 44.4 kb 0.1%
Other Assets 213.1 kb 0.3%
Levels 38.8 mb 57.1%
Scripts 55.6 kb 0.1%
Included DLLs 2.6 mb 3.9%
File headers 12.4 mb 18.2%
Complete size 67.9 mb 100.0%

Why are the levels so large? Shouldn’t the instancing, and use of hierarchies result in small file sizes? Also, why are teh file headers so big?

Thanks,
Johnny

If you’re using static batching, then a large combined mesh is built and included with the level.

We have recently received this question thru our support system, and we are in the process of enhancing the documentation. I’ll copy the answer here since it will help other users searching for this our community:

File headers is data that is kept maintaining references and settings for the assets, such as resource assets. It is the amount of extra data apart from the “raw” data contents in a file. Do you have assets in the “Resources” folder? You can try moving some or all files out of this folder and see if that reduces the file headers.