Electronic Navigation – ‘Unfolding’ Electronic Charts

Source: Mariner's Learning System, By Captain Bob Figular

Almost all electronic plotters include the same kind of capabilities for creating and storing waypoints that are found in GPS receivers. They have an important advantage, though, in that you don’t have to enter waypoint positions in terms of their latitude and longitude coordinates; there is a much simpler procedure for creating waypoints graphically, in effect by just pointing at the chart image and telling the plotter where you want to go.

At present, electronic charting is still in the process of rapid development; different manufacturers use different types of cartridges and discs, with different software and different keyboards and control panel layouts. With this said there are a number of processes that are similar and common to all chart plotters.

Zoom in / zoom out are self-explanatory terms referring to the way in which the scale of the displayed image of the chart can be changed. From the user’s point of view, zooming is usually a very simple process.

Scrolling and panning are ways of moving the screen image to make different areas visible: scrolling generally refers to a north–south movement and panning to an east–west movement. Many programs also include different ‘centering’ options that allow you (for instance) to lock the center of the display to your own position. Other options allow the user to choose whether to view the chart in the conventional ‘north-up’ mode, or to turn it round to ‘course-up’ mode.

Decluttering is only available on vector charts. In effect, each type of information is stored in a different database: contour lines in one; spot soundings in another; major lighthouses in another; buoys in another; and so on. The effect is rather as though a paper chart were built up using many different layers of tracing paper, each of which can be removed or replaced at will. Most software programs add and remove some layers automatically as you zoom in and out, in order to stop the screen becoming cluttered. Many, however, allow you to choose ‘more detail’ or ‘less detail’, or to make your own selection of exactly what kind of information you want to see. It’s important to realize that the accuracy of information depends on the scale of the original chart, not on the zoom level you happen to have chosen, and to be aware that it is possible to inadvertently hide information, which could turn out to be important.