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ECDIS will use IMO-standardized formats, but some chartplotters require specific data formats. A charter may use one or both types of ENC:
* Raster Charts: The chart plotter displays a "picture" of a paper chart or map which is referenced to geographic coordinates. A [[GPS]] position can be displayed upon the raster chart, but accuracy depends upon many factors including the type of projection (e.g. conic or mercator) used in the original chart, and the reference system used (e.g. [[North_American_Datum|NAD-27]] or [[World Geodetic System|WGS-84]]).
* Vector Charts: The chart plotter constructs a facsimile of a chart using raw data from a data base. The major advantages are a reduction in the amount of data to be stored, and the ability of the chart plotter to identify certain features (such as water depth) and act upon them (e.g. do not allow the ship to run aground)
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