O is for OMPHALOS

From the Greek word for navel, the word was used to describe the navel, the boss of a shield, and the center of the world.  A conical stone was used to mark supposed locations (see example below).

Omphalos from Delphi*

This mythic conception of the omphalos seems to be identical with the idea of a world pole or axis mundi, which can be conceived of as an umbilical cord or as a phallus.  The center of the world is important as a cultic site and as the point of entry into this world in origin myths.  In your world creation, starting at the center is useful and natural way of delimiting a culture or civilization both in terms of both physical and mental geography.  I would consider having it as a marking a portal to the underworld or, if I was using something like the Yggdrasil as the axis mundi, I'd have it be a planar gate into the pathways between worlds/planes.

* More here.