I don’t think those are decks. Look how big they are - the Death Star is the size of moon. If those horizontal lines are meant to be decks, they’d be miles high. I suspect that the actual inhabitable layer, much like actual planets, is (relatively speaking) an extremely thin skin. Like you say, those layers appear to have depth. If the interior of the Death Star is all power generators and giant lasers, what we’re seeing there is probably the superstructure intended to support the industrial heart of the Death Star, not the inhabited exterior.
Of course a weapon used to destroy planets can be equally effective against mile long capital ships. But the Death Star has several strategic weaknesses in a space-superiority role. It’s big, slow, expensive and can only be in one place at a time. Basically it’s value is in either terrifying the inhabitants of a planet when they see a brand new moon in their sky, or obliterating them.
The Empire is unlikely to encounter a fleet of ships large enough and concentrated enough to justify using a Death Star to fight them off. For most capital ship battles, their fleet of star destroyers are more than adequate. If space superiority was the objective, the Imperial Navy would have just commissioned a hundred Executor class super star destroyers instead of a Death Star.
But more and bigger capital ships wouldn’t be effective against the Rebellion. The Rebels would simply run away and hide among the Imperial population. The Empire had to build a weapon that sent a clear message. "If your planet engages in Rebellion or harbors rebels, it will be destroyed. Ergo, while the Death Star is certainly effective against capital ships, the real strategic value is as a terror weapon.
The Death Star looks like it’s constructed like a “globe”. That is to say, the structure consists of latitudinal, longitudinal and radial elements.
As silenus indicated, they have artificial gravity. They can orient the actual rooms any way they like.
While most of the “inhabital” zones would be near the surface, I’m sure a lot of the interior not occupied by machinery and whatnot is inhabitable as well, if only to provide access for maintenance purposes.
One thing I should point out. In both Death Stars, when ships land at the docking bays along the equator, the decks are oriented along the latitudinal axis.
Wasn’t Han’s first ref to it (ANH) something on the order of: “but there’s no planet here, just that small moon” or am I misremembering the qualifier “small”?
Current space science within our own solar system shows that many moons are tiny compared with Earth’s own GIANT natural satellite.
That’s no [giant] moon! Still very very big, that much is certain.
Which is addressed in the passage I quoted from the Tech Manual.
The Death Star was definitely a terror weapon rather than a tactical one. It’s purpose was to be big, bad and intimidating.
According to Wookiepedia, the Mk II was 900 km in diameter.
Oh come on, even a not-really-fanboy who has only seen the movies, like me, knows that the Emperor dissolved the Senate even before the Death Star Mk I was destroyed.
Which isn’t to say there weren’t contractors crawling through the Imperial Ship Design paying off anybody they could, just that they could skip the middlemen in the (Late) Senate.
Fun fact: The low circular orbit around a spherical primary has a period that depends only on the primary’s density. So if your back-of-the-envelope assumption was that the Death Star has about the same density as the Earth, then it was inevitable that you’d get the same orbital period as low earth orbit.
Can we all agree that it’s still insignificant next to the power of the Force?
The Force is 99.9999% about giving a tiny nudge in the right place at the right time. The Death Star was as subtle as a wrecking ball. It’s a matter of perspective which is truly more powerful.
Yeah, but let’s not forget the Force took out the entire Death Star using a single missile… and then did it again for the hat trick.
The Death Star managed to take out one planet full of pacifists. And then exploded. 
The real reason for the MkII was that Palpatine declared, “Yeah? Well I’ll build a BIGGER Death Star! With blackjack! And Hookers!”
Ancient religions and magical tricks are no match for laser blasters. Lando, Nien Nunb and Wedge took out the second Death Star with good ole fashion mad flying skilz. Let’s give credit where credit’s due.
Yes, I referenced your quote.
I think the real reason is that, from a filmmaking standpoint, if ships were to “land” on the Death Star like one might land an aircraft on an actual moon, it would be a lot less visually impressive than the Millennium Falcon “driving” up to a miles high indentation in an sheer vertical wall that extends as far as the eye can see.
Which reminds me, is the trench the rebels flew along in the finally of Star Wars supposed to be the same trench that’s along the equator? It looks a lot smaller.
It isn’t. The thermal exhaust port was near the “North Pole” of the Mk I.
Yeah, visually you really have to have the external flight decks lateral to the DS. They’d already done the “up from beneath” shots with the various Star Destroyers, so they needed a different perspective for this shot.
I really know waaaaay too much about this to be healthy.
Was Zapp Brannigan in command?
Lee Iacocca.