A city in a province adjoining an ocean will have been founded on the best spot for an ocean port. The ocean will only be accessible through the port city in this case, and not through the surrounding region.
Plain [ae48], plain, in region Tollus Routes leaving Plain [ae48]: ... West, to Ocean [ae47], Tymaerian Sea, impassable Inner locations: Carim [em28], port city, 1 day
Note that from the province surrounding the port city, access to the ocean is not possible.
Carim [em28], port city, in province Plain [ae48] Routes leaving Carim [em28]: West, to Ocean [ae47], Tymaerian Sea, 1 day Out, to Plain [ae48], 1 day
However, ships may sail into and out of the port city itself. From the Tymaerian Sea, this looks like:
Ocean [af48], ocean, in Tymaerian Sea Routes leaving Ocean [af48]: North, city, to Carim [em28], Tollus, 1 day South, to Ocean [ag48], 3 days ...