When you have as much room as you want to grow, you're gonna want to grow out. The Frontiers are the regions of space that have not yet been fully colonized and are usually very dangerous but rewarding.
The systems that each race has stemmed from, highly industrialized regions with dense populations and heavy law enforcement. Very safe and still plenty to do, but not where you go if you're after adventure.
Worlds that have for whatever reason lost contact or broken ties with the rest of civilization and have descended into a more primitive style. Most are quite dangerous and exclusionary, and those who show magic are usually shunned and/or killed.