Elucidation: A one-dimensional continuant fiat boundary is a continuous fiat line whose location is defined in relation to some material entity. Example of usage: The Equator; the median sulcus of your tongue; the line separating the outer surface of the mucosa of the lower lip from the outer surface of the skin of the chin.; all lines of latitude and longitude; all geopolitical boundaries. (Axiom label in BFO2 Reference: [032-001]) https://www.ebi.ac.uk/ols4/ontologies/bfo/classes/http%253A%252F%252Fpurl.obolibrary.org%252Fobo%252FBFO_0000142