IHO S-57

IHO S-57 is the International Hydrographic Organization standard for the transfer of digital hydrographic data, and its product specification defines the Electronic Navigational Chart (ENC), the official vector chart an ECDIS reads. Edition 3.1, issued in November 2000, is the version in service and has been frozen since then: no new features will be added so that hydrographic offices and ECDIS makers work to a stable target. An S-57 ENC encodes depths, contours, navigational aids, and hazards as objects with attributes, which the ECDIS draws and queries. S-57 is being superseded by the S-100 framework and the S-101 ENC specification, but frozen S-57 ENCs stay valid through a long coexistence.