So how large is the Enterprise-D? Well, numerous sources list the ship as being 641 metres long, give or take a metre. According to the TNG TM co-ordinate system given on page 20, the port edge of the saucer section has the XYZ co-ordinates -27987,0,19418 - making the beam 2 x 279.87 = 559.74 metres.

However, this does not fit in very well with scale diagrams of the ship - even the one used to demonstrate the co-ordinate system itself! These uniformly yield a beam in the region of 470 metres.

For what it's worth, the DS9 TM entry on the Galaxy class gives a length of 642.51 metres and a beam of 463.73 metres. But it also gives the ship a height of 195.26 metres, which is a good 50 metres too high - at 195.26 metres, each of the 42 decks would be 4.65 metres high, which is far above the accepted deck heights.

In any case, the consensus of opinion seems to be that the ship is about 470 metres across - far too large to fit even the largest possible interpretation of the size of Spacedocks doors. We don't get a really good straight-on view of the E-D coming through the doors, but the saucer seems to clear the sides with about 20% to spare. This would make the doors about 590 metres across.

Since the makers used the same model for both stations, then we know that everything else on the station exterior is scaled up in size also. We get a ratio for the size of SB 74 to Spacedock of 2.3 : 1, giving SB 74 a diameter of 8,781 metres and an overall height of 13,360 metres.

This makes the station one of the largest we have ever seen in Trek - for that matter, amongst the largest in sci-fi as a whole. While structures like the Dyson Sphere or the Star Wars Death Star dwarf SB 74, the likes of Babylon 5 - which is five miles long - would just about fit into SB74's docking bay if it could get through the doors.

I know many people don't like the "scaled up design" idea much, but it can in fact work quite well so long as you stick to direct multiples. The biggest problem is in exterior windows, but in fact these are usually (not always) less than half the height of a given room. If we make one ship or structure exactly twice the size of another, then it is relatively simple to say that the windows on the uprated ship are twice as large compared to the decks, and that only every other deck has windows. This can work reasonably well with a 2x scale up - a 2.5 foot high window would be reasonable on a spacecraft, and a 5 foot window would still be reasonable. A 3x scale up can also work - our 2.5 foot window would end up as 7.5 feet, still within the deck heights of most ships. A 4x scale up pushes the limit, with 10 foot high windows - essentially we end up with a window that occupies the entire visible wall. For scale ups greater than 4x, we need to start increasing deck heights significantly and things start to get tricky from there.

Starbase 74's 2.3x scale factor indicates at least two possibilities :

Firstly, there could be a two-for-one deck substitution. Since the scale ratio is not an integer, the decks themselves would be higher in SB 74 by 15% - say from 3.75 metres to 4.3 metres. This would indicate that the later Starbase has significantly more headroom than the earlier Spacedock.

Alternately, there may be a three-for-one deck substitution. In this case each deck would be scaled down to 82% of its original value. If the original Spacedock had deck heights of around 4.5 metres, then Starbase 74 would have decks of 3.45 metres. This would indicate that the later Starbase has significantly less headroom than the earlier Spacedock.

Personally, I lean heavily toward the first idea. It's established in epsiodes such as "Relics" and "Trials and Tribbilations" that Starfleet accomodations have improved greatly over the last century or so, so more headroom certainly makes more sense for a later design. A two-for-one deck substitution also makes the windows a more reasonable size in both stations.

Apart from the sizes, almost everything else in the specs page is pure guesswork, since we know so little about these stations. Given that the station is a 2.3x scale up of Spacedock, its volume will be over twleve times greater. I have scaled up the crew by rather less than this, to provide for the far more luxurious accomodations which we could expect in a structure like this. Armament is scaled up by guestimated factors that just felt right to me.