Abstract: Apparatus providing an aid to navigation comprising two circular discs which are superposed and rotatably mounted with respect to one other, the upper disc presenting a transparent zone corresponding to a geographical area, for instance a closed stretch of water, with indication of some coastal places or localities. The latter disc carries moreover a peripheral circular graduation divided over 360.degree., the "0" point of which is situated to the north of said geographical area. So far as the base disc is concerned, its upper face is provided with parallel straight lines and carries two indexes situated at the ends of the diameter parallel to these lines. It is sufficient, to determine the course to be followed for travelling from one of the indicated places to another, to rotate the rotatable disc with respect to the stationary disc to bring the points corresponding to these two places to lie on one and the same line of the set of parallel lines.