In days of old no mariner worth his salt left home without an armful of marine charts tucked under his arm and a magnetic compass in his pocket. Today, most marine charts are in electronic format and more than likely displayed on a marine GPS device, a chart plotter or combo marine electronics device.
So what is marine chart and how do you use one?
Simply put, charts are topographical maps of the sea or inland water region. There are actually two formats, raster and vector. A raster marine chart consists of digital images that show you geo-referenced features. That means you can see your boat’s position on the charts in reference to other features to figure out, for example, how far you are from dry land. You can get regularly updated raster charts from NOAA. The common format for raster marine charts is called Raster Chart Display Systems (RCDS) and this is the format NOAA uses. So if you want NOAA raster chart updates you will need a chartplotter or marine chart display system that is RCDS compatible. (NOAA stands for the National Oceanic and Atmospheric Administration. It is a government organization responsible for oceans and the atmosphere).
The second format of marine charts is the vector chart. Vector charts are a combination of the digitized paper marine charts that can be overlaid with objects and information accumulated in a database. It has taken NOAA years to build the vector charts but they are now to a point that more and more chartplotters are opting to use them. The common format for NOAA’s vector charts is called Electronic Navigational Charts or ENCs. NOAA provides the ENCs free of charge and updates are also free. To take advantage of ENCs your chartplotter must be ECDIS capable (EDICS stands for Electronic Chart and Display Information Systems).
ENCs include real-time information such as current tides, precise coordinates of channel limits, and other geographic information designed to simplify navigation and make collision avoidance easy. NOAA has completed vector chart information on all the major ports in the United States and they continue to refine information on smaller ports. As with raster marine charts, you can download updates from NOAA as they add data.
Using Raster and Vector Charts
To use raster and vector marine charts you need a third party commercial software product that knows how to process and display the charts. Most chartplotters and GPS plotters use one or both types of these charts. What’s better, raster or vector? That’s up to you, the raster contains less information but to date is a more complete set of charts. The vector charts, while still in process, have made a lot of progress in the last few years and are updated weekly so the database is continuing to expand on a regular basis. You will most likely be able to obtain updates directly from your chartplotter manufacturer but it’s always worth knowing that the option to download directly from NOAA gives you up to the minute detail as soon as it becomes available.