There are 9 galaxies in every universe. Each galaxy contains 499 solar systems. The first number of any set of coordinates relates to the galaxy.
Each solar system contains 15 slots for planets, plus one uncolonizable slot, Outer Space. Each planet may have a debris field and/or a moon. This allows for a total of 67,365 possible planet locations.
Each galaxy is a distance of 20,000 units from the next and previous numbered galaxies.
In order to get an overview of the whole systems and the player's locations, the community founded user-projects like ogame.gamestats.org, where everybody can help to create a huge map.