1. A method of synthesizing an intervisibility image consisting of pixels and representing the distribution, over a terrain overflown by an aircraft, of the zones of direct intervisibility between the aircraft and at least one potential threat, that is to say of the places visible in respect of the aircraft, wherein, on the one hand, a safety plain color is associated with the intersection between the aircraft's visibility sector and the union of the zones of direct intervisibility and, on the other hand, a danger plain color distinct from the safety plain color is associated with the part of the aircraft's visibility sector exhibiting an empty intersection with the union of the zones of direct intervisibility, and in that, in at least one mode of the method of synthesis, said plain colors may be modulated at each pixel by a shading cue (αsha) representative of the relief of the terrain at said pixel.