A simple inexpensive optical projection map display is described which converts the range and bearing signals available from ground-based beacon aids such as TACAN or VOR/DME into a continuous map indication of present ground position without additional computing. This provides an area navigation system from such aids within their limits of accuracy, which increases with decreasing range from a beacon.

The display, which is self-synchronous, employs a series of circular map micro-transparencies, each of which is centred on a TACAN or co-located VOR/DME beacon and which can be changed in flight. The transparencies are automatically orientated with reference to beacon magnetic north on insertion, by a notch in the rim. The transparency is rotated by the bearing signal and is translated radially by the range signal to give a continuous indication of present position.