vernacular division
Names people use for parts of a place, with edges nobody has ever fixed by an authority.
A vernacular division is a division whose areas are named in common speech without an authority defining them. Residents agree on the name and on roughly where the area lies, and disagree about the edges, because no boundary was ever set.
Such an area is recorded by its name and a point rather than a boundary, and where a boundary is stored it is an approximation someone drew, not a surveyed line. Two vernacular areas may overlap, and a place may sit in one for some residents and in another for their neighbors.
An administrative division carries the same kind of name but the municipality maintains the boundary. Where the name is in use and the boundary exists only in a stored approximation, the division is vernacular.