Visibility analysis plays a crucial role in the planning process and for the acceptance of renewable energy projects. There is a need for visual impact analysis in Strategic Environ­mental Assessment (SEA), Environmental Impact Assessment (EIA), Impact Mitigation Regulation (IMR) in state-wide, regional and municipal/local planning pro­cesses. In plan­ning practice, basic methods for visibility analysis are often used, without knowing about the validity of the specific analysis. We empirically investigated how DEM/DSM reso­lu­tion, accuracy and precision, GIS software package and algorithms used, re­presen­tation of the impacting object, and other factors influence the validity of visibility analyses. Based on our results, we conclude that the validity of visibility analyses and thus the whole sub­sequent visual impact analysis can be significantly increased by carefully choosing the adequate visibility analysis approach.