@misc{_M_[1938],
 copyright={Public Domain},
 address={Gotha},
 journal={Vogels Karte von Mitteleuropa. Fliegerkarte},
 howpublished={online},
 year={[1938]},
 publisher={Justus Perthes},
 language={ger},
 title={M 32-NW Köln},
 type={Image},
 URL={http://www.rcin.org.pl/igipz/Content/210105/PDF/WA51_190993_PTGC61-12-r1938_M-32-NW-Koln_0001.pdf},
 keywords={topographic maps, aerial maps, Cologne (Germany; region)},
}