Known Space is the complex of solar systems linked by 'holes'.
'Adjacent' solar systems may be in different galaxies or may be only a handful of light years apart.
Every time a new hole found, Known Space expands.
A hole can only be 'jumped' if a Mulligan field is generated. Either the hole is 'gated' or the ship carries a Mulligan drive. Most travel is by ships without Mulligan drives along gated routes.
The search for holes and the exploration of the solar systems they link was initiated by Centre, a complex of six solar systems that is now the political and topological core of Known Space.
•	The Borders are up to 10-25 standard days' travel from Centre.
•	The Inner Fringe is about 25-50 standards days' travel from Centre.
•	The Inner Fringe is about 50-200 standards days' travel from Centre.
•	The Far Fringe is over 200 days' travel from Centre.
Not all shipping routes are radial from Centre; over the millenniums other strings of holes have been explored.