BSB (or BSB/KAP) is a file format used primarily for the storage and transmission of nautical charts. Although the format is commonly known as "BSB", the main file extension is actually .kap (or sometimes .cap), though .bsb files can also optionally be used. The main image data (as raster images) is found in .kap files, possibly with multiple images in separate files being part of a multi-page chart. The .bsb file, if present, has additional data pertaining to the chart as a whole. Additional metadata is contained in associated text files, generally stored with .bsb.txt and .kap.txt double extensions, or else names ending in "_bsb.txt" and "_kap.txt".