It's with some difficulty that I describe the City.
Now that you have the size of the City in mind, now imagine that said city has an endless number of 'floors,' each one separated by almost indestructible walls, known only as Megastructure, kilometres thick at it's lowest points, sometimes perhaps hundreds of kilometres thick. And if you go anywhere near Megastructure, it will instantly trigger a safeguard response. The safeguard are pretty much the automated defense system of the City which went haywire prior to the story.The City is a Dyson sphere with at least the diameter of Jupiter's orbit. But it's not a shell. It's FILLED with city, presumably all the way down to the sun. There might not even BE the sun in it's center any more.
There is a room in the City the size of Jupiter. But it's empty. Different layers of the City (it's a bit like an onion) are blocked by layers of material known as Megastructure. This material laughs at gigaton level explosions. Loudly.
The whole structure weighs in at a ludicrous 1.2 million SOLAR masses. That's right, it weighs 1.2 million times as much as the sun.
If it were made out of air. But it isn't.
You can get almost anywhere by walking, or climbing stairs, if the elevators don't work. You will walk a LOT.
I found a nice image on Wikipedia which illustrates just how utterly fucking mindbogglingly stupendously HUGE the City is. It will kinda put things into perspective.
Comparison of size of Betelgeuse (largest dull-red sphere inside Jupiter's orbit) and R Doradus (red sphere shown inside Earth's orbit) together with the orbits of Mars, Venus and Mercury and the stars Rigel and Aldebaran to scale. The faint yellow sphere centred on the Sun has a radius of one light-minute. The yellow ellipses represent the orbits of each planet. [The massive sphere roughly represents the size of the City.]
If you try to attack Megastructure, or even get near it, depending on how hard you are attacking the wall, you could trigger a massive safeguard response resulting in pretty much endless level 9 exterminators literally spawning all around you. Now this may not sound impressive, until you consider that mid level safeguard carry swords that pretty much fuck with reality and spacetime or somesuch, as well as carrying pistols that cause what can only be described as megaton or gigaton explosions (as a side note, said pistols barely scratch the surface of Megastructure).The Safeguard are a program independent of the netsphere. The netsphere was designed as a means of providing service to those who could log on. However, the netsphere was thrown into chaos (the actual reason is not exactly known, but the prequel manga NOiSE implies that a small group of humans is at fault) and the Safeguard changed their modus operandi from preventing unauthorized users from entering the netsphere to killing off anyone who does not possess Net Terminal Genes. The Safeguard have nine levels of hierarchy, Level 9 being the most powerful. However, their Exterminator (originally the lowest level safeguard) system has a different form of hierarchy where "First Class" is the most powerful.
Now apart from all of the ridiculously powerful defense systems, the sheer size of the city alone could send most factions into starvation before they even happen to find any enemies to fight. Since the city is basically endless vertical floors with walls and walkways etc., the only real way you could get ships through is by bombarding Megastructure to try and open a hole.
If anybody is more familiar with the structure than I (as I've just recently started reading the manga), then feel free to correct me on this if any information is incorrect.
Now, which faction in sci-fi would be able to take over the City, if they were happened to have been dropped right into the middle of the City? Please don't make this boring and instantly say 'Culture or Xeelee.'