A type of electronic navigational chart (ENC) format. The S-57 digital chart is a vector format based on the S-57 object model. This model defines hydrographic information as a combination of descriptive and spatial characteristics. Within the model, these sets of characteristics are defined in terms of objects separated into a feature and a spatial part. The feature part of an object contains descriptive attributes and no geometry, whereas the spatial part mainly contains geometry of type vector and may have additional descriptive attributes.
These objects are independent of the actual representation on the screen. This information is provided separately. An S-57 electronic navigational chart is also called a cell which has a defined geographical coverage and navigational purpose or usage. A cell is a rectangle, i.e. defined by two meridians and two parallels and its data not exceed 5 Megabytes. The data of cells of same usage do not overlap making a continuous chart display possible. The chart data in S-57 format is usually digitised from a paper or a raster chart, or may be created directly from the survey data and object databases.