Section 5

Plotting Basics

Waypoints

Waypoints are intermediate points plotted to support a passage. Waypoints are usually used in conjunction with the American Global Positioning System (GPS), or other satellite navigation systems.

Waypoints and the paths to and from waypoints can be plotted to avoid hazards, or find the quickest or most desired route to a location.

The Latitude and Longitude co-ordinates of a waypoint are taken from the chart and entered in the GPS device so that it can provide the straight-line path or track to the waypoint. This is usually expressed as a True compass direction, which may, or may not be the same as the boat's heading due to leeway or current.

Waypoints provide a safe route to the entrance of an anchorage. The co-ordinates of each waypoint are entered in the GPS unit. The device can then display the route to follow between waypoints.

Plotting and labeling the route is helpful to make sure the planned route avoids any hazards.

See Sail Canada plotting and labeling of a Waypoint

GPS Basics

A GPS unit can find its location in three-dimensional space to a useful and reliable level of accuracy. This position is given as co-ordinates (and altitude), or displayed on an electronic map or chart. This position can usually be used to plot a fix with acceptable accuracy.

Smart phones have GPS capability, with many navigation applications available. There are also many brands and models of GPS units specifically for maritime use.

GPS Accuracy

The accuracy of a position acquired by GPS can be affected by atmospheric or solar conditions, interference from objects or other signals, system errors, satellite positioning and availability.

In populated areas, the GPS signal can by augmented using WiFi, cellular and other systems to provide better accuracy. Optimum accuracy may not be available to boats sailing or motoring in more remote areas. The Canadian Coast Guard expects standard augmented GPS accuracy of within 10 metres, 95 percent of the time.

Visit the Canadian Coast Guard's website for GPS Information.

GPS and Paper Charts

When using GPS with paper charts, it's important that the GPS unit is matched to the same horizontal datum as the chart. Most units designed for maritime navigation have this capability. Mismatched datum can result in location inaccuracies.