In Shayla's time, the official Imperial census records 523 inhabited systems.
These are spread unevenly through a disc of space roughly two thousand light years across and five hundred light years thick. This is a tiny fraction of the galaxy, which is a hundred thousand light years across. To give some perspective on what this means for travelers, the fastest ship takes about two months to cross from one border of human space to the other.
Of course, inhabited systems account for only a tiny fraction of stars in this region of space. The common convention, other than for navigational charts, is for maps to show only inhabited systems and to ignore the vast numbers of stars in between.
Just over half of these systems are under the control of six Grand Families, either directly ruled, or through long-standing allegiances. The Family Skamensis is the strongest with 83 systems. The Family dom Calvino are the paupers at the table with a puny 27.
The remaining systems are independent, or owe only transient allegiance, but with these six power-hungry sharks in the pool, independence is difficult and precarious. Some worlds are strong enough, either individually or by banding together, to keep the Grand Families at bay. At the other extreme, many "outworlds" on the periphery of civilization are too small and remote to be worth subduing.
A privileged few, the Freeworlds, maintain their neutrality by treaty. Freeworlds usually have a dedicated purpose, or charter, and establish themselves as highly specialized centers of excellence for academics, artists, or artisans. The Families are prepared to honor the Freeworlds' independent status in return for the strictly impartial value that these worlds bring to all of humanity.
It is no coincidence that Freeworlds also typically lack natural resources worth fighting over.