Milky Way Galaxy
The Milky Way Galaxy is a large spiral galaxy, approximately 100,000 Light Years across. The Central core is approximately 3,000 Light Years deep with a supermassive black hole in the center ("Sagittarius A*" using Terran nomenclature).
There are two known powerful energy barriers in the Milky Way. The first discovered surrounds the outer edge of the galaxy, protecting it from intergalactic space. The second surrounds the inner core, approximately 1,000 LY around Sagittarius A*. Both have been breached with varying effects upon the crews of the vessel.
The Milky Way is subdivided into 4 Quadrants.
The United Federation of Planets straddles the Alpha/Beta Quadrant border. The Klingon Empire and Romulan Star Empire both lie primarily in the Beta Quadrant, while the Cardassian Union resides within the Alpha Quadrant.
The Milky Way Galaxy contains millions of habitable worlds and thousands of sentient species and spacefaring cultures. The following is a political map of the Alpha and Beta quadrants, focused on the relationship of interstellar states to the United Federation of Planets.