The paper presents a concise description of the basics of a mathematical model and a computer program for calculating the characteristics of complex grounding systems. The use of such a program is particularly interesting in the analysis of the grounding system of electrical installations in an urban area in which there is also a high-voltage cable network. The analysis of such a system requires the formation of a model that should contain the grounding devices of electrical installations connected by high-voltage cables as well as the grounding of the associated distribution networks in the observed area. To illustrate the use of the program, some characteristic results of the calculation of the grounding system in Zadar and Split are presented in numerical and graphical form.