Electronic Charts
NOAA free electronic chart downloads use a format different from chartplotters. NOAA Charts are Raster format and are intended for computer software programs such as Maptech, Nobeltech, The Captain, etc., which means that the are, for all intents and purposes, sort of like photographs of a real NOAA paper chart. Chartplotters, on the other hand, use a vector chart format. There are major differences in the two formats. A raster chart which is re-oriented, say 180 degrees on your computer screen, will display the same way as a paper chart turned 180 degrees. All the feartures, printing, etc. would be "upside-down" on your computer screen. A Vector chart would display notations, symbols, labels, etc. right-side up no matter wheather you are usin North up, Course up or track up . However, the Vector chart eliminates much "un-necessary" chart information to decrease the screen re-draw time and to observe the limits of the memory capacity as well as the processor speed. For example, if you compare a raster and a vector chart for the same location one of the most obvious differences is that many of the land features have been eliminated. Also, the shore line is "less then exact" and is sort of a cartoon version - for lack of a better analogy - of the raster chart. There are other differences. The important thing is that they are not interchangeable. The vector chart is not readable on a PC while a raster chart is not readable on a chart plotter - at least for now. Things ARE changing all the time, however, I don't expect this issue to be resolved in the near future. Your free NOAA raster chart downloads must be read by computer software. Let's take Maptech Region 3 (Cape May, NJ to Nantucket) for example. This package comes bundled with a series of raster (NOAA) charts along with Topographic charts and a lot of very valuable nav photos at a price of about $300.00. It also includes the opperation program "Offshore Navigator". That is the important part of the program which allows you to read ANY(!) downloaded NOAA Raster Chart - from any region. In other words it is not necessary to purchase the Maptech program for each Maptech region; you only need one to read any NOAA chart. Of course you will not have the benefits of the topo and nav photo charts for the regions you do not purchase. Once you have the Offshore Navigator program you will be able to plan routes, waypoints etc. at home on you PC and then download the digital information into your chartplotter, providing you purchase the chartplotter/PC power/USB cable. (The Maptech program has an interface for all the major manufacturers). The interesting thing is that you will see major discrepancies between the two formats. I have created routes on raster charts which show my boat going over land on the vector chart, and visa-versa. I have also transfered a rout that I actually ran with my boat onto both chart version and showed that I went "over" land masses. Which one is more correct? Well you can't count 100% on either, as they both have errors. Hence the disclaimer by all chart publishers. The GPS is actually more accurate then either version of the chart.There is no cheep way around it; if you want to use the raster charts for planning, or even as the master to your on board nav system and still want a chartplotter at the helm, you will need both formats. The good news is that the Garmin chartplotters which will be released very soon (a matter of weeks) will contain preloaded vactor charts for the entire USA. You will not have to purchase chips unless you leave the country.Sorry for the length of my response but there is a lot of confusion on this issue.Good luck, Pat