- - There are basically two different chart systems in use - "Raster" e-charts that are nothing more than scanned photos of real paper charts/acetates and "Vector" charts that are human interpreted copies of real paper charts.
- - The original e-charts were all Raster and the files were enormously large. If you have ever seen the computer directories of the original Maptech
digital charts you will see up to a hundred subdirectories each with megabytes of chart data. This first format of e-charts consumed so much hard drive and CD space that only a few charts could be stored and used.
- - Then the "Vector" chart format was invented where instead of recording/storing every little pixel of a scanned paper chart, only the screen
locations of significant points on the chart were recorded and straight lines connected these points. You can observe this system on the little GPS displays with mapping. As you zoom in your will see shorelines depicted as straight lines with one shade/color on the land side and another shade/color on the water
side. Virtually no shoreline detail is present. The file size of Vector charts is dramatically smaller than Raster.
- - In order to get hundreds, even thousands of charts on a CD, chart producers hired people to sit at a desk with a paper chart and use a plotter stylus to "pick" significant points which the computer connected with a straight line. Unfortunately, the "boss" kept bugging the worker to hurry up and get the chart done. This lead to the omission of quite an amount of significant data in the finished Vector chart.
- - An article in Ocean Navigator about a decade ago outlined the problem when an ocean liner ripped a long tear down it hull
because of lack of complete information in the existing Vector charts. The chart translators were seeing a square of 4 or so depth sounding that were numerically equal and then placing only one data point in the center of the group. That can be an expensive and fatal mistake as each sounding on a paper chart is specific to the exact Lat/Long of its placement. What the depth is in between is unknown as the two equal depth readings could be on the sides of a sea mount with the peak of the mount uncharted.
- - Fortunately, the process of transcribing the original paper/acetate nautical chart to a Vector format has significantly improved since those days so more data from the original chart is being shown on the Vector version. However, if you really Zoom in on a Vector chart you will see the large loss of detail that is present on paper or Raster charts.
- - It was just a marketing
decision that in order to make compact Chart Plotters both small and economical only the Vector chart system could be used for chart data storage
. Trying to store terabytes of raster chart information on a little handheld GPS plotter or any other size plotter was a non-starter.
- - So, Yes, Chart Plotters cannot contain the detail and mass of content that a paper chart conveys to the nautical navigator. Whether you actually need all that extra detail that paper charts present is a different discussion.