I found answers to most questions I've had since starting online, including what the white/purple "?" means on the zone list for what pokemon are in the area.

 

What I can't find any information on is what the circles under them mean. In some zones they're yellow (and obviously mean "available") but purple ones are sometimes with white question marks, other times a purple circle is with a purple question mark.

 

What's the difference between these circles mean?

The circles under them are green/blue indicating that they either spawn on the ground/grass (green) or in the water (blue).

On extra note, Pink ? means a Membership catchable Pokémon.

If the circles under them is blue, it means they spawn in water and if they are green it means they spawn in ground. If they have white question mark, it means you can catch them even if you don't have membership and if they have pink question mark it means you can only catch them if you have membership.