S-57 format digital maps are more than a simple photocopy of the printed maps (like raster maps), they represent a database containing a detailed description of each object (beacon, wreck, survey system, fire area, regulated zones, etc.). Users can sequence map data and use smart access functions depending on the type of navigation and zone, while reducing volume (approx. 1 Mb for one map).

Maps are assigned to 6 categories depending on scale:

Cat. 1: Overview < 1: 1,500,000

Cat. 2: General 1: 350,000 - 1: 1,500,000

Cat. 3: Coastal 1: 90,000 - 1: 350,000

Cat. 4: Approaches 1: 22,000 - 1: 90,000

Cat. 5: Port 1: 4,000 - 1: 22,000

Cat. 6: Mooring > 1: 4,000

The map's category is indicated in its identifier: the category is the first figure after the two letters for the country.

Unlike printed maps, which exist for a given geographic scope and scale, one single digital map can cover the full range.