Cyrodiil is 16 sq. miles.
This figure comes from Bethesda's PR department.
The Oblivion Construction Set tells us that each exterior cell is 4096 units by 4096 units or 192 feet by 192 feet or 58.5 meters by 58.5 meters. I count approximately 86 cells from Topal Bay south of Leyawiin up to the invisible border north of Cloud Ruler Temple. 192 x 86 = 16,512 feet. 5,280 feet = 1 mile and 3 miles = 15,840. So, north to south, Cyrodiil is approximately three miles long.
I count 104 cells west to east, from Anvil to the invisible border east of Sundercliff Watch. 192 x 104 = 19, 968, or less than 4 miles.
Because Cyrodiil is eccentrically shaped (i.e. it narrows considerably) over on its western end there's some guesswork involved when estimating total square milage. I put the total at 9 square miles and I think that's being pretty generous.
For comparison's sake, Vvardenfell is approximately 6 square miles. I've not yet counted cells in Skyrim but I plan to very soon. I suspect that Skyrim is between Cyrodiil and Vvardenfell in size.
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I'm not fond of using speed as a measurement of game world size because speed is relative. And, as Acadian points out, so is timescale. But since the title of the thread is
how big is Cyrodiil for us I think, in this particular thread, player speed and timescale are both perfectly valid considerations.
Skyrim seems smaller for sure.
I felt the same at first. After I got rid of my compass and had to start using landmarks I have to say the game world began to feel larger to me. In addition, I've recently begun phasing out my map as well. Now
that has had a really significant effect on how large I percieve the game world. Skyrim has seemed to almost double in size. I get lost a lot, now, and boy, there's nothing like getting lost to make an area (real or virtual) feel
enormous.
::EDIT:: A friend directed me to a mod tonight that removes all of the markers from the map. So I'll probably go back to using the map for awhile (without markers) and see how I feel about that. I just took a look at it and I have to say, the 3D map is actually very pretty when it's not covered up with markers.
several aspects of Oblivion's landscape was randomly generated during development, this isn't up for debate. it's why 99% of the dungeons are completely generic and uninteresting.
First, it cannot be said that Cyrodiil's generation is "random." Bethesda had specific topography in mind that they wanted their software to reproduce (i.e. Cyrodiil as shown in maps). They also used selective geological data. They were very speicific about what they wanted to achieve with their software. The result is anything
but random. And, as BAugustus points out, once that process was finished Bethesda's world builders proceeded to alter the generated landscape by hand. We do not know to what extent they altered it but I suspect some areas were handcrafted more than people realize.
Second, as glargg mentions, dungeons are a separate issue. Anybody who thinks Oblivion's dungeons are 'cookie cutter' or 'clones' of each other needs to take a trip to UESP and look at dungeon floor plans. Not one is the same. I am actually very, very impressed with the ingenuity of Bethesda's dungeon builders. They have done a marvelous job with limited resources.
Now it's true that in Oblivion dungeon tilesets are limited. But that limitation applies to every 3D game I have ever played. Time and money constraints mean that a limited number of meshes can be created for each dungeon type. If you want a game in which each and every dungeon looks unique you will have to play an isometric game with dungeons that are 2D paintings.