Source code question - Somewhat technical

[Antiporcupine]

Okay, I'm having trouble understanding a couple of things in the source code, and I was hoping someone who has worked with this could help. What exactly are the nodes and the subsectors? I can't seem to find concrete examples of these, and I can't figure out why a level with, say, 10 sectors can have 26 subsectors. Can someone help? Thanx.

 

[TheDarkArchon]

NODES on the Doom Wiki
Subsectors on the Doom Wiki

To understand this, you'll need to know the basics of how BSP rendering works. (BSP on Wikipedia)