Yeah, model reuse makes sense as a major factor here. Probably also texture reuse, though, as it would be rather hard to use the same texture on multiple models, while using the same model in multiple places, by definition, implies the same texture unless it is specifically set up otherwise.
One thing about the TES editor is that it makes it very easy to throw together a few premade pieces, and get a level that looks okay and plays well, perhaps within an hour. This, I would assume, makes quickly prototyping a level very easy, and making it look unique can be accomplished by going back later and dropping/rotating/scaling in a few rock models here and there, to give downwards cave slope #5 over there a unique layout as it restricts the usable path so something that winds through about six large rock formations which are actually just three models, one of them used more than once.
And all of that could theoretically fit in a few kilobytes for a small level(Would depend on how many bytes are used for each piece, and I'm going to guess that it is less than one hundred), plus the base cost of the models which are already used tens of thousands of times elsewhere anyway. Meanwhile, the custom-made corridor in the other game might use a unique variation of the wall textures, with some peeling wallpaper bits here and there to make it visually less repetitive, making just a few steps worth of level take up ten times the space.
For a quick bit of real facts, I just checked Portal 2, and it has 2.5 GB for maps alone. Now, Portal 2 (and, really, all Source games) uses a map format where the map is created from a combination of blocks that are chopped up, stretched, textured, and otherwise manipulated into looking like something, alongside numerous models and props included by reference and thus taking up very little space. Of course, Source also precalculates all of the lighting, collision, and visibility data and saves it alongside the map, another thing that takes up space.
For comparison, Morrowind. The main game (no expansions or mods) has two main files describing the levels: Morrowind.bsa, 300MB, contains all of the models and textures (and perhaps other things? Not audio or movies, those are stored separately, each taking about 250MB, including both expansions), while Morrowind.esm, just under 80MB, contains all of the descriptions of items, levels, NPCs; scripts, quests, and all of the gameplay data in general.
Now, the final numbers: Portal 2 has 5GB of music, sound, textures and models, and 2.5GB of actual level data. Morrowind, a significantly less detailed game, has a bit over 500MB of that stuff, and all of the levels share a mere 80MB with the damage values, game scripts, dialogue scripts, race definitions, and every other bit of gameplay description for the entire game.
Different styles that work best for different games, I suppose, as Portal 2, and clearly MW3 put more into unique environments where no two levels look very similar, while Morrowind, Skyrim, and Oblivion obviously take the route where the same hallway may be re-used many times, but the gameplay and clutter within it make it unique from all of the others in the world, merely providing the physical structure that contains the actual important parts, the story and gameplay.
(Disclaimer: 172% of the statistics and facts in this post have been made up or estimated based on a complete lack of meaningful evidence. Use at your own risk.)
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Topic: Game size... what the hell is going on here? MW3 vs. Skyrim (Read 7700 times)