The Guild of Navigators is a group of highly proficient magic users dominant in the port cities. They are the only ones who can be trusted to safely navigate a ship to Delphik's hidden harbours, and hold a monopoly on the business. They are relied upon by people ranging from merchants, to kings.
The Guild earns money by allowing ship's captains to hire their Navigators, often for a decent sum. Onboard, depending on the journey's objective, Navigators may perform a variety of tasks from being an actual navigator and cartographer to military advisor.
Over time, the areas near the ports became so saturated with magic that most of the inhabitants had some inkling of magic or other. This allowed them to become far more proficient mariners than those from non-magical ports. Nonetheless, some inevitably are (as everywhere else) more attuned to the flow of magic than others; though navigating is not traditionally recognised as pure magic, young students are recognised by their powers of memorisation and an instinctive knowledge of the movements of the sea, and weather patterns.
If their skill is proven (by a test. Most of the time, only rich families are able to provide sufficient tutoring for their children; poorer children tend only to find their way into the Guild if they are orphans "adopted" by the Guild, a practice slowly growing out of hand) the child is initiated into the Guild of Navigators, first as an apprentice, then as a Navigator.