A subsector is 8 hexes by 10 hexes, or about 26 lightyears by 32.6 lightyears.
(You can run reasonable campaign in a subsector, but given the range of Jump drives, it may feel a little cramped.)
A quadrant is two subsectors wide and two subsectors tall, or 16 hexes by 20 hexes, or about 52 lightyears by 65 lightyears.
(You can run a reasonable long-term campaign in a quadrant.)
A sector is two quadrants wide and two quadrants tall, or four subsectors by four subsectors, or 32 hexes by 40 hexes, or about 104 lightyears by 130 lightyears.
(You can run an expansive campaign in a sector, or several, as your heart desires.)
A domain is two sectors wide and two sectors tall, or four quadrants by four quadrants, or eight subsectors by eight subsectors, or 64 hexes by 80 hexes, or about 208 lightyears by 261 lightyears.
(In my opinion, the domain is the largest practical setting size for 95% of the campaigns that most Referees will run, unless you are doing a Grand Tour scenario and only showing off the occasional world on a long trek through multiple sectors.)
Note that the sizes above barely even scratch the surface of the universe as we know it. The Milky Way galaxy is 100,000 lightyears across, or so I was taught in school so many years ago. (I'm sure that's been changed, but EDG is a much better source of up-to-date astronomical thought than I am.) That's 481 domains across, and 383 domains tall.
And the universe is much, much larger than that.
For all practical purposes, you could easily get away with a quadrant, a sector or a domain for your campaign, and have plenty of opportunities for gaming over the course of one or multiple campaigns.
Does that help?
With Regards,
Flynn
