The universal applicability of UAVs (Unmanned Aerial Vehicle) in the civil and commercial sectors offers enormous potential to transform urban and rural infrastructure, improving efficiency and effectiveness while reducing associated costs. For the successful operation of a remotely or autonomously controlled UAV, satellite navigation plays a crucial role in ensuring stable and reliable air navigation. One of the oldest and probably best known navigation satellite systems is the U.S. Global Positioning System (GPS). Unfortunately, many cyber attacks against UAVs are strongly associated with civil GPS vulnerabilities. The market growth of UAVs and the vulnerability of GPS are leading to more critical flight movements near or in no-fly-zones, which in turn has significant safety risks in a dynamic and complex environment such as aviation. In this paper, an experimental GPS spoofing system was developed and implemented for geospatial guidance of UAVs around predefined no-fly-zones using an algorithm to determine the shortest feasible path. For this reason, a cyber attack analysis of GPS was performed first. Followed by the theory and application of fake signal generation and emission in laboratory environments. Based on the obtained and valuable knowledge, three corresponding algorithms for real time spoofing, shortest way spoofing and UAV no-fly-zone were elaborated and implemented. Finally, the developed geospatial guidance algorithm is illustrated in a real life scenario to show the problem by entering critical areas.