“30 years of Card/1 - Anniversary event in the north; [30 Jahre Card/1 - Jubiläumsveranstaltung im Norden]” (2015) gis.Business | issn : 1869-9286, 16(1), pp. 15–16. Available at: https://journal-gis.business/index.php/gisb/article/view/500 (Accessed: 8 November 2026).