I made this post recently.
You have 4 “review pools” that, if you want a continuous supply of reviews, you should be careful not to overlap them.
- Bonus - you can set this location. In theory, this should be a place you’re familiar with, but it practice many people choose a big city to try and help dig it out, a rural area to feel like they’re making a difference, a vacation area, maybe a place they’re going to visit soon or have recently. Or they “trade” with someone. Sometimes staff schedules times for us to reset the bonus area, indicating they aren’t particular about us being “trapped.”
- Home - this “should” be your home town but it’s very much like an American philosophy where people move away from where they grow up. People practice it similarly to above and there are times staff allows us to reset this location setting.
- Local - you can’t manually change this. It’s based on where you last played and Ingress takes priority over Pokémon GO - meaning that even though I live in the US and played GO Fest Madrid (Spain) last year Wayfarer didn’t give me Spain nominations until I actually logged into Ingress. Note that “local” might not feel local to you - it’s a fairly big region and the area should be represented on your “featured” page may still be a few hours away.
- National - this is based on your “local” area. You could end up reviewing anything nominated within your country and sometimes slightly across the border - especially if you live in Europe. Similarly, territory is included so things like US Vırgın Islands or British Vırgın Islands pop up when applicable. The national pool includes Upgraded nominations and other nominations prioritized into the system.
I had a really nice explanation of this written up on the old Wayforum. It was archived and could be found, but I think some of it may be inaccurate, now, since I reference review regions and being able to review edits has changed that dynamic.
Please 
reality check me if I got something wrong, above.