Fun Fact 24: Any fiction or game involving space on a scale of even a tenth of the galaxy is meaningless because it's so huge. There are at least 100 billion stars in our galaxy. Which means if in your guidebook you detailed each star system with just one page of text, and you can fit
269 pages in an inch of book thickness with one solar system on each side of a page, the book would be almost 3,000 miles tall. Earth's diameter is almost 8,000 miles.
If you were to read that book at one page per minute, continuously without sleep 24 hours a day 7 days a week, you would finish over 190,000 years later.
And this is one page of text per solar system. Go ahead and try defining our solar system, including Earth and all its biology and civilization and history, in just one page.
I say this scale is meaningless because our stories involving galaxies always focus on just a few people and planets, and even then only on extremely limited parts of those planets.
You could easily tell the story of Star Wars without anyone in the cast visiting more than a half-dozen solar systems. You have just a few scattered planets visited, a moon or two, a couple bars, etc. In a stretch you could set it in just one solar system.
In terms of a game, just try designing, even in a crude overview using randomized tables like in Traveller, just one quadrant of a galaxy. It's pointless.
And unless you hit all those places, you might as well not even talk about the galaxy at all. It's just a buzzword that makes the fans titter.