I don't know how Golarion does it. I have this ability firmly rooted in the Eldest.
In my homebrew the Eldest are the only constants in a sea of change. This makes them at once both all-powerful and nearly insane. Imagine if your entire world around you was defined by constant change and you are the only one who can't.
As such the Eldest have the will to impose form on the formlessness around them. In their fevered minds they envision a "perfect" land and each Eldest creates this differently. There was Mad Queen Mabbe who imagined a world of mirrors where all would look upon her beauty and despair; there was the Red Queen who had the mind of a 6 year old mortal girl and envisioned a "Wonderland"; then there was Luposz, the Werewolf Lord, who saw only an endless land of pinewood and night.