1. Free Software Foundation. (2021). Free Software Foundation (2021). Retrieved from https://www.fsf.org/
2. Grassmuck, V. (2004). Freie Software. Zwischen Privat-und Gemeineigentum: Bundeszentrale für politische Bildung.
3. Haklay, M., & Weber, P. (2008). Openstreetmap: User-generated street maps. IEEE Pervasive Computing, 7(4), 12–18.
4. Kurt Menke, G., Smith, R., Jr., Pirelli, L., & John Van Hoesen, G. (2016). Mastering QGIS. Packt Publishing Ltd.
5. Leidig, M., & Teeuw, R. (2015). Free software: A review, in the context of disaster management. International Journal of Applied Earth Observation and Geoinformation, 42, 49–56.