An Electronic Chart Display and Information System (ECDIS) is a computer-based navigation system which is used to visualize digital nautical data, as an alternative to paper nautical charts. Nautical data includes all information which may be of assistance for the safe navigation of vessels at sea and harbors, such as sea depth information, positions of buoys, lights, wrecks, and so on. The data to be rendered can be either vector or raster data.
Data for vector-based ECDIS systems are distributed as cells, called Electronic Navigational Charts (ENC). Each ENC cell contains nautical data for a specific region, ranging from very large regions, such as parts of oceans, to small regions, like berthing areas inside harbors.
Multiple ENC cells may be grouped into a catalogue. Catalogues are useful for the efficient distribution and processing of ENC cells: they provide an index of all their ENC cells, together with the spatial extent of each cell. This allows for the efficient retrieval of geographical data for a specific region and scale, without the need to scan each individual ENC file.