Feature Type

Administrative regions are mapped with the boundary=administrative tag on boundary relations that reference ways that mark all or part of a boundary between two neighbouring areas. To allow consistency of tagging worldwide the administrative boundary type is indicated by a numeric admin_level whose national 'translations' are indicated on the page for boundary=administrative.

The use of relations means that there need only be one way per border rather than multiple overlapping ways, and avoids some issues that occur with really long ways. For editing relations of this sort use of one of the more advanced pieces of editing software is highly recommended (e.g. JOSM).

As with any addition please make sure that the source you use is suitable for use in OSM.