@misc{_Ravenstein's_[ca,
 editor={Ravenstein, Hans (1866–1934). Oprac.},
 copyright={Public Domain},
 address={Frankfurt a/M.},
 howpublished={online},
 year={[ca 1926]},
 publisher={Geographische Verlagsanstalt u. Druckerei Ludwig Ravenstein},
 language={ger},
 language={pol},
 title={Ravenstein's Karte der Provinz Ost -Preussen und der Freien Stadt Danzig},
 keywords={political-administrative maps, East Prussia, Ermeland, Masuria, Free City of Danzig},
}