An unmanned aerial vehicle (“UAV”) receives location information describing geographic boundaries of a polygonal no-fly zone (“NFZ”), the NFZ having a plurality of virtual walls each associated with a geographic line segment. The UAV identifies a closest and a second closest virtual wall of the plurality of virtual walls of the NFZ to a geographic location of the UAV. The UAV determines a first distance from the location of the UAV to a portion of the closest virtual wall nearest to the location of the UAV and a second distance from the location of the UAV to a portion of the second closest virtual wall nearest to the location of the UAV. In response to the first and/or second determined distances being less than a threshold distance, the UAV modifies a velocity and/or a trajectory of the UAV such that the UAV does not cross the virtual walls.