It can be thought out logically. Issues like:
1. Job
2. Cost of Living
3. Proximity to family
4. Local culture
5. Environment (City vs suburbs vs rural vs coastal vs mountain vs plains vs cold vs hot vs dry vs wet, and so on)
If I was free to relocate, those are some of the issues I would consider before doing so. If I had children, which I don't, I might also consider the education system and social services like health care.
Basically, go where you will be happiest.