Astrometrics

This site is a direct lift of the text from The Warp Zone's Stellar Cartography section, which itself is a life from Star Charts.

Star Charts

For general stellar mapping purposes, the Milky Way Galaxy is commonly divided into four equally sized, cubic quadrants, defined by one meridian passing through the galactic core and a second one perpendicular to the first, that also passes through the galactic core. These four quadrants are referred to as the Alpha Quadrant, Beta Quadrant, Gamma Quadrant and Delta Quadrant. The United Federation of Planets and its neighboring powers, including the Klingon and Romulan Empires, are located in the Alpha and Beta Quadrants, whereas the Borg Collective is located in the Delta Quadrant, and the Dominion in the Gamma Quadrant.

For more granular charting purposes, the Milky Way Galaxy is further divided into subquadrants and sector zones. The subquadrants are 36 wedge-shaped slices of the galactic disk, each one 50,000 light-years long, 3,600 light-years high, and 8,727 light-years wide at its widest point, representing a 10° arc of the galaxy. The sector zones are a set of 10 concentric circles each 5,000 light-years wide and 3,600 light-years high centered on the galactic core.