By Ben Ellison
Electronic Harbor Buddy
SoftCharts digital charts are raster, whereas C-Map and Navionics charts are vector. Basically, raster charts are simple pictures of familiar paper charts, while vectors are tracings turned into databases of chart information, then displayed as graphics by the plotter.
Raster charts are created by scanning the official works of hydrographic offices, and some users favor them because they show every detail and nuance laid down by the original cartographer. It takes tremendous effort for the various private vector shops to convert all these details into mathematically defined lines, symbols, and text, but the results take better advantage of the processing power of plotters (and onboard computers).
The pros of vector start with cleanly drawn lines and letters and solid colors. Data is layered, so elements can be turned on and off for clearer presentation on smaller screens or when zooming out. Numbers are real, so depths can be shown in meters or feet, even fathoms. Vectors can be turned course up, and all the soundings and labels will remain right side up--nice for comparing to a split-screen radar image. Also, data can be attached to any object on the chart; you'll learn to move the NavNet cursor over a buoy or port information symbol to get a small pop-up data window and access to a full page of information.
The cons are that "noncritical" data is left off of vector charts to make the tracing process less expensive. You won't see much of the shoreside information that you get on a paper or raster chart. There is also the possibility of error in the tracing process. I've seen such errors, though minor and in remote areas. Watch out for those! Lastly, vector charts are ultimately drawn by a machine and thus lack some of the little niceties a real cartographer is capable of--like placing an island name just where it won't get in the way of other data. In my opinion, they don't look as good.
C-Map has recently introduced a new vector specification called NT+ that includes numerous valuable improvements, and Navionics is planning to introduce its own new data format "soon." It's also worth noting that new ways of mixing and blending cartography seen in the latest Nobeltec and RayTech products suggest that the functional differences between raster and vector will eventually fade away. --B.E.
Got a marine electronics question? Write to Electronics Q&A, Power & Motoryacht, 260 Madison Ave., 8th Fl., New York, NY 10016. Fax: (917) 256-2282. e-mail: PMYElectronics@primediamags.com. No phone calls please.
This article originally appeared in the January 2003 issue of Power & Motoryacht magazine.