The blue circles are not capture zones, they indicate towns and areas where players can spawn. If members of your team are located within the area of a blue circle then that town or area will be listed as a respawn point under “Towns” in the respawn menu.
If there are more enemy in the blue circle than there are members of your team then the area will be blocked for you to spawn on until your team has more players than enemy there. The spawn point will still be listed in the respawn menu but it will display how many friendly and how many hostile players are within the circle.