In astronomy, in the galactic coordinate system, the Sun is the center. North is above the galactic plane and south is below the galactic plane. East is right of the sun, and west is left of the sun. The galaxy is divided into degrees, both latitude and longitude.
According to "The Explored Galaxy" star chart, I know that Delta Vega is located near the galactic edge. Furthermore, I know that the galactic barrier as at the edge, and that extragalactic space lays outside this barrier. In the episode "Where No Man Has Gone Before", there is this line:
Approaching galaxy edge, sir.
And using as a yardstick the distance from Sol to Alpha Centauri, the edge is less than 30 light years from Sol according to this chart.