@misc{UBHD-1427829, author={Heeroma, Klaas}, title={Kaart 21 - 30}, publisher={Van Gorcum}, address={Assen}, year={1963}, pages={Kt. 21 - 30}, language={dut}, library={UB [Signatur: 65 D 28 ML] ; DE [Signatur: <DE> Kartenschrank::Oost-Ned., Kt.3]}, }