More work on the old routes to Rimward

I thought a lot about this last night, as I was going to sleep.

The Varala Drift seems like an area that is an unexplored frontier, yet surrounded by systems to Rimward that have multiple settled colonies and major worlds?

How could this be?

So I came to the idea that in the initial push to the Rim, worlds that were prime colonization sites, clean atmosphere, water, etc, got larger populations, and huge starports. Other worlds had native populations.

I have the idea that those non-human worlds that invented their own interstellar travel technology pushed out from their own homeworlds, settling those stars around their origin worlds.

I am reworking my maps with that alien expansion in mind.