Vector Inspector

If you run back and forth to the same familiar harbors each weekend, then you probably have little need for an electronic chart display (ECD). But if you enjoy coastal cruising and exploring new territories, the value of an ECD is immeasurable. An ECD not only saves you time when plotting courses, but when interfaced with a GPS or loran, it shows your exact location on a chart, along with your past track and intended course. This information is extremely valuable when cruising unfamiliar waters, and it's even more valuable at night or in fog. Still, an ECD is only as good as the electronic charts it displays, and so this month we took a detailed look at C-MAP's C-Cards versus Navionic's NavCharts to decide which brand is better, and why. But first, a little background information.

There are two types of electronic charts; raster and vector. Raster charts are optical scans of printed-paper charts, and they look just like them when viewed on a personal computer screen (you can only view raster charts on PCs). Vector charts--like those made by C-MAP and Navionics--are digitized representations of paper charts, and they can be displayed on typical marine ECDs and plotters. (If you're considering an ECD, keep in mind that the unit is designed to use either C-MAP or Navionics chart cartridges, but not both.)

In general, vector charts have some distinct advantages over their raster-scanned counterparts. Since their data is stored in layers, vector charts let you to select the type and amount of chart information you want to see, and they may contain additional information not shown on paper charts, such as detailed Lights List information or a directory of services found in a particular harbor. And for the ultimate navigation setup, vector charts can be rotated from a north-up to a course-up orientation on your ECD, so their display will correlate closely with what you see on your radar for easy cross checking (the ECD shows you where you are, the radar shows you where everybody else is).

How They're Made And How They Work

The data in any vector-chart cartridge is a section of each manufacturer's worldwide database, and the area covered by any cartridge depends on the memory capacity of the cartridge and the complexity of the area involved (more harbors take up more memory). But perhaps the biggest factor that determines the type of data you get is the way the database is put together in the first place, and C-MAP and Navionics take different paths here.

In contrast to just a few years ago--where both companies would create electronic charts by digitizing (electronically tracing) paper charts by hand--C-MAP and Navionics now begin the process with a raster scan of a printed paper chart, and then they convert that scan to a vector format so you can see and manipulate the data on your ECD. They also correct their vector charts (add/delete buoys or wrecks, change light characteristics, etc.) according to any changes listed in the Notice To Mariners that were published since the paper chart was originally printed. That explains why vector charts may differ from--and be more up-to-date than--a paper chart of the same area.

C-MAP starts with a raster chart from BSB, which are actual NOAA charts stored on CD-ROM. At a computer workstation, the raster chart is converted to vector format, and items like land areas and intertidal zones are filled in automatically on the new vector chart. Then--using a process unique to C-MAP--an optical character recognition program kicks in and picks up all of the depth soundings found on the raster image, and they're stored on the vector chart. Next, a technician manually types land labels onto the chart, but detailed descriptions of items like bridges, shoal areas, and obstructions are hidden from view, accessed only through menus.

It's a different story for navaids like buoys and lighthouses. In this case, when you move the cursor atop a navaid symbol, a data box pops up and identifies that marker automatically. More detailed information about the mark is available through the menus, and in all cases the description of the mark comes directly from the U.S. Coast Guard Lights List..

In contrast, Navionics starts by making its own scans of NOAA charts, and the entire manufacturing process is done in-house for complete quality control. The actual digitizing of the charts is done in much the same way as C-MAP, but with several important distinctions.

First, Navionics charts do not have information hidden in menus. Rather, chart details such as bridge type and vertical clearance are shown right on the chart, so you don't have to dig for the information. In addition, Navionics adds "local knowledge" onto its charts, so in Newport, Rhode Island harbor, for example, you'll see numbers along the shore line that represent marinas, restaurants, and other shoreside points of interest. A directory of those facilities is also shown right on the chart.

Though buoy and light information will also pop up automatically on a Navionics chart, the company does not record all depth soundings when making its charts. Rather, it only includes depth contour lines and random "spot soundings." This means the water areas on a Navionics chart are less cluttered, but they don't contain all the depth information found on a C-MAP chart of the same area.

Results--General

To evaluate C-MAP vs. Navionics charts, I looked at their coverage of five locations around the country--Newport, Rhode Island; Annapolis, Maryland; Tampa Bay, Florida; Seattle, Washington; and Chicago, Illinois--and compared them with the NOAA paper charts of the same area. I used Northstar's 951X to view Navionics charts, and Magellan's 6500 to display C-MAP.

The first big difference between C-MAP and Navionics is the way buoy and other navaids appear on screen. The Northstar shows Navionics’ buoys as dark circles with a "G", "R", "W", or "N" notation inside (G=green light, R=red light, W=white light, N=general navaid like nun or can). Put the cursor on a circle, and up pops the buoy's description which matches the description on the paper chart.

C-MAP, on the other hand, assigns graphic symbols to navaids, so a nun looks like a nun, a can looks like a can, and so on. While this was helpful in quickly seeing the type of navaid in question, the downside was the symbols are outlines, not solids, and so they were sometimes hard to see against a background covered with depth soundings.

Another major difference has to do with the data shown at various zoom levels. On a wide-area paper chart of the New York City area, for example, the waters of Long Island Sound will be solid blue with no buoys since you need a more detailed chart to navigate those waters. In making its charts, C-MAP does the same thing--if there are no buoys shown on a wide-area paper chart, they won't appear on a C-MAP chart at the corresponding zoom level.

But Navionics takes a different approach. In creating its charts, the company often "pulls" major buoy or lighthouse symbols up from detailed charts so they will appear on screen at a wider-area zoom level. Put another way, at a 16-mile range you might see a lighthouse and sea buoy on a Navionics chart, but it won't appear on a C-MAP chart until you zoom in to a closer range. The result? You get to see the big markers further out in the zooming process on Navionics charts, and this is a plus since it will reduce the amount of zooming you'll have to do when creating long-range routes on your ECD. But then again, coastal running is just one use of electronic charting. Getting you safely in to the harbor and alongside the dock--even in fog--is a much more important one, and C-MAP and Navionics differ here as well.

Results--Specific

In order to check each charts' detail, I zoomed in from 16 miles down to 1/4 mile in the five harbor areas mentioned above. Essentially, what was true for Newport was true for all areas I checked, and C