Wałek, G. 2013. Use of Quantum GIS and SAGA GIS software to build digital elevation model of Grajcarek catchment. Acta Universitatis Lodziensis. Folia Geographica Socio-Oeconomica. 14 (Mar. 2013), 133–144. DOI:https://doi.org/10.18778/1508-1117.14.10.