Mercator

Mercator refers to the Mercator projection, the chart projection long used for marine navigation because it preserves angles. On a Mercator nautical chart, a straight line represents a constant compass bearing, or rhumb line, making it practical for plotting courses between waypoints.

For boaters, Mercator charts simplify route planning, pilotage, and offshore passages by allowing bearings to be transferred directly between chart and compass. However, scale changes with Latitude, so distance and shape distortion increase away from the equator. Navigators should use correct chart scales, verify positions with GPS, and review routes on a Chartplotter.

Mercator is closely related to electronic charting and weather overlays, where forecast data, waypoints, and routes must align accurately on the displayed map. In PredictWind, understanding projections helps when comparing forecast layers, routing outputs, and GRIB data with the charts used onboard.