How do world events become active?

Whenever I am in an area, I feel like the nearby world events tend to be active. I am wondering if the mechanics have world events only become active near players, if being near a location with a world event makes it have a higher chance to become active, or if world events just become active randomly throughout the world and it is just more common for them to start some places than others (for example, the corkus ones seems to be active quite frequently).

 

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Wynn Plains has the highest frequency