Actually, this circles are science stations (some for science, some for security, some for weaponry and so on).
They are all scattered across the inhabitable island full of weird stuff. So we can make it pretty interesting.
1. Try to get to central station and hold it. (Various bonuses on your own section).
2. You can go from station to station or using jungle passes.
3. Some interesting and complicated bonuses with various resources/control points.
Here is the precise map of the island with legend:
- Click image to enlarge.