The purpose of the Geographic Notice is to transmit information that pertains to a region or area, for example a security zone, an area of fog, or dredging operations. The areas that are being defined can be circles, rectangles, polygons, or sectors. They can also be defined as a simple point or series of points (polyline). The Geographic Notice message can be made up of multiple subareas in which case the total area is the union of the subareas. This message can also be used to convey advisory lines or tracks (using the polyline subarea); however, the Route Information message should be used for recommended or directed routes.
A Geographic Notice should be used to broadcast dynamic information (i.e., information that is time-dependent). These messages are to be used for a specific time period, and will automatically timeout at the end of the period. If the Geographic Notice must be in place longer, then a new Geographic Notice must be transmitted with a new start and end time. It should be only used to convey pertinent time-critical navigation-safety information to mariners or authorities, and not as a means to convey information already provided by official nautical charts or publications.
Gregory Johnson (gwjohnson@alionscience.com)