The efficacy of conventional remotely-sensed satellite imagery for regional geological mapping is greatly reduced in northern Ireland due to the extensive vegetation cover. Imagery produced from digitally processed geophysical data sets is an extremely powerful technique for the acquisition of geological information in such terrain. Directional filtering of gravity and aeromagnetic data allows the major structures to be delineated clearly. Pseudo-illumination from the northwest shows the main Caledonian structures: Tempo-Sixmilecross Lineament; the Omagh Fault; the continuation of the Southern Uplands Fault and the en-échelon character of the Fair Head-Clew Bay Lineament. A synergistic display of the geophysical data sets shows the major lithological boundaries, variations within individual lithologies and subsurface geological features.