I'm glad the pylon issue has been raised - it's certainly a weird point in the construction of a Starship!
Regarding the in-universe naming of these decks, it only really occurs in three episodes:
: Kirk’s cabin is on this deck [i.e. 12] (apparently) and has a decent stretch of corridor adjoining it. As has been repeatedly pointed out, there is no way to squeeze this all into the pylon (horizontally anyway - thanks Timo
for your usual skill in bursting the envelope!)
: Rand’s quarters are blatantly on this deck (G. T. Fisher calls for aid from an intercom) and even more corridor is visible prior to this on Evilkirk’s drunken ramble to her door. Regarding this ramble, why is Evilkirk even here? The presence of Rand’s cabin seems to take him almost by surprise, just a fortunate opportunity to be taken advantage of. I would postulate that he is going back to his cabin and just happens to pass her own along the way. In fact, at this point in the series, “Deck 12” is almost being treated as the main deck of the ship, hardly suitable if that deck were situated in the pylon neck.
Dagger Of The Mind
: Here, Van Gelder is spotted on Deck 14, having (apparently) exited the Transporter Room and started roaming the corridors. There is not indication that he ever used a turbolift – if he had, wouldn’t he have gone somewhere more secluded? Or if his ultimate destination was in fact the bridge – why not there? To detour via the pylon neck is an odd choice, even for him! ...
So, if the lower saucer rim deck is deck 7 (personally I think deck 5 is more accurate but that’s another debate) then the pylon takes on decks 8, 9 and 10, leaving the Engineering hull to begin fresh at deck 11. Deck 12 is then situated slightly down into the secondary hull, plenty of space for everything seen on screen!
If the pylon neck decks end at deck 10, this is similar to the lowest of the saucer decks. Maybe the emergency separation actually occurs at the bottom of the pylon instead of the top? This would have the added bonus of keeping all the numbered decks together…
I just realised, this last bit has been thought of before, in the Star Trek Officer's Manual:
(click for link to full size - thanks to http://www.cygnus-x1.net
for this resource)
This seems to be the thread I was looking for and I hope Mytran forgives that I'm cannibalizing his post as a starting point.
A long time ago I was biased because of the diagram in The Star Trek Officer's Manual
believing that saucer separation would require a section of the neck to come along with the saucer, I now believe this to be different and its just the saucer that separates, leaving the engineering hull with the neck section behind.
The Making of Star Trek
only provided deck numbers for the primary hull and deck 11 was the lowest, no deck numbers were given for the engineering hull (I believe for TMP the lowest one for the engineering hull was 18 or 19).
Therefore, I believe the engineering decks start at the top of the neck or pylon section with engineering deck 1. According to a cutaway I did back in the 1980's (I used the pylon's / engineering hull's windows as reference for deck height) I arrived at 18 engineering decks and decks 12 and 14 would just be in the middle of the engineering hull and there'd even be windows that could match the windows of Kirk's provisional quarters (while his own were renovated; this is "Mudd's Women" that just takes place shortly after WNM and everything
is in the process or just recently has been upgraded) - one is circular, one rectangular (on the port side the windows may just be square...).
Then why don't they say "engineering deck"? Since there are no decks exceeding deck 11 in the saucer, deck 12 can only be an engineering deck.
Then why doesn't Spock say "engineering deck 2" in "Enterprise Incident" when he accompanies the Romulan Commander to her quarters (in the neck)?
In "Conscience of the King" Kevin Riley stole a phaser from "H deck". "The Doomsday Machine" established that the shuttlecraft hangar is not just on deck 1X but that this entire engineering deck is labeled "hangar deck" - or "H deck".
"E deck" might be the deck with the "Engineering Section" (not to be confused with the "Engine Control Room" in the saucer) and deck 2 in the saucer might also have an alphabetic designation. Thus the turbolift computer understands that Spock wants to travel to engineering deck 2.