Borderextract is an osmosis-plugin used to extract different levels of administrative borders as polygons from an openstreetmap-dump or database. openstreetmap contains detailed administrative borders, like country, state or village borders. these borders are represented by ways, and held together by relations tagged as admin-borders.

borderextract can combine these border-pieces to closed polygons. this enables reverse-geocoding, thus one can easily query for the administrative area(s) a particular coordinate is in.