USCG General Navigation

IALA Maritime Buoyage System defines cardinal marks by their light rhythms. Each quadrant is assigned a specific number of flashes, such as VQ or Q for North, and varying combinations for East, South, and West, allowing mariners to identify the safe side of a hazard based on the light's characteristic.

The National Geospatial-Intelligence Agency (NGA) produces charts for foreign waters, including Canada, while the National Ocean Service (NOS) is responsible for U.S. coastal waters. This division of labor ensures global coverage for U.S. mariners under the authority of the Department of Defense and Department of Commerce respectively.

Magnetic directive force is the horizontal component of the Earth's magnetic field. Near the magnetic equator, the lines of force are parallel to the Earth's surface, providing maximum horizontal intensity. Conversely, near the poles, the lines of force are nearly vertical, significantly reducing the directive force on the compass needle.

Mean Lower Low Water (MLLW) is the average of the lower low water height of each tidal day over a 19-year National Tidal Datum Epoch. It serves as the official chart sounding datum on NOAA nautical charts.

Under the U.S. Aids to Navigation System, bridge channel centerlines are marked by a red-and-white vertically striped diamond or octagon shape. This visual aid assists mariners in identifying the safest passage through the bridge span, ensuring they maintain a central position to avoid structural hazards or shallow water.

The compass card is divided into 360 degrees. North is 000°, East is 090°, South is 180°, and West is 270°. NNW lies halfway between North (000°) and Northwest (315°). Calculating the midpoint (000 + 315) / 2 yields 337.5°, which is the standard bearing for a NNW heading.