Quake3World

I was just curious, really. But from a technical perspective, what is the difference between a map for Quake 3 and a map for Quake 2?
More in terms of the engines rather than the games themselves per se.

What kind of restrictions does one face that the other doesn't? What requirements does one have that the other doesn't? Are there different practices that have to be observed when creating a map for one over the other?

I would imagine that at the very least Quake 3 maps raise some technical limitations for how big the maps can be, which I assume would be true across many different metrics. But I'm wondering what other changes were made between the two.

Elsewhere on the internet I saw someone talk about expanding a particular open engine to support Quake 3 maps. That struck me with a lot of questions, and perhaps some of them could be answered with a better understanding of Quake 3 maps. One thing that struck me was how (at least with Quake 1 and 2 maps) the maps were completely enclosed, so if you tried to import a Quake map into this engine, you'd have geometry with no openings for the player enter the map from; you'd only be able to use the Quake map in its entirety rather than importing it as if it were a complex piece of geometry. Or is this not an issue with Quake 3? Are the old requirements for VIS done away with in Quake 3; does Quake 3 handle visibility differently?
I'm also curious if there are other reasons why someone would specifically seek to import Quake 3 maps into another engine, as opposed to later Id Tech maps or even just "anything you could create with radiant."

I'd say it's the IBSP version. Quake 1 uses different version, Quake 2 uses next different version than Quake 3. As you may know, Quake 3 uses version 46 (which is noted as integer hex 2e in the map bsp file). So you may guess out that earlier games used earlier versions of IBSP format (IBSP stands for Improved Binary Space Partition, as opposed to Binary Space Partition found in DOOM). So maybe this could be the difference. the format itself was developed across games, each version using different features. You may know that Quake Live uses version 47 (integer hex 2f in bsp file), and has an additional lump for advertisements, which makes it even more different than previous versions...

I didn't know that, but would have guessed something to that effect. But what difference does version 46 have from what was used for Quake 2 and/or all the other Quake 2 engine games, like Sin? Does the new version carry any new features? What kind of things can Quake 3 IBSP do that Quake 2 could not?

I'm not an expert on BSP file formats, but one obvious difference is the support for curved surfaces, which was introduced in idTech3 (the Quake 3 engine)