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 A navigational chart is defined as being "an official database made by a government-authorised hydrographic office (HO)". There are two type of electronic chart - raster and vector.
Raster charts are flat images; essentially just "scans" of traditional paper charts. They display no other data other than that visible to the eye and appear distorted or pixelated if viewed at a scale other than that at which they were compiled. They can be used by an ECDIS in the absence of vector chart coverage, in a reversionary mode known as RCDS (Raster Chart Display System), although there are additional requirements to operate in this mode.
Vector charts exploit the definition of a chart being a "database" in a more literal sense. Data is always present, but what is displayed is customisable by the user/ECDIS software. This allows for objects on the chart to conceal data until interrogated - thus making a simpler display. The ability to configure the display does also means that safety-critical information could be concealed. Conversely, there is also the risk that an incorrectly configured system will display too much data and over-complicate the display from the user's perspective.
Official vector charts are known as Electronic Navigational Charts (ENCs) and are the only charts that can be used with an ECDIS to allow the host vessel to go paperless or "digital". ENCs must conform to standards stated in the IHO S-57 publication. Furthermore, ENC development and encryption is detailed in IHO publication S-63 and the display format standards can be found in IHO publication S-52.
ENCs are held by one of the two Regional Electronic Navigational Chart Coordinating Centre (RENCs), located in Taunton, UK and Stavanger, Norway. Distributors such as ChartCo and Jeppesen then provide ENCs to end-users.
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Electronic Charts
