BSB File

What are BSB files and how to open them

Are you having problems opening a BSB file or are you simply curious about its contents? We're here to explain the properties of these files and provide you with software that can open or handle your BSB files.

What is a BSB file?

A .BSB file is a MapInfo Sea Chart file.

MapInfo Sea Chart files are part of the BSB/KAP system used for storing full-scale nautical charts as raster images. The "BSB" component serves as a documentation-oriented file that describes one or more panels ("KAP" image files) that together make up a complete chart. Its purpose is to link metadata - such as chart name, edition, projection, scale and georeferencing - with the image panels, so that chart plotting or navigation software display the raster chart accurately.

The chart image panels themselves are stored in companion KAP files. Each KAP holds an image section (the map graphic), preceded by a plain-text header containing key values like "VER/" (version), "BSB/NA=" (chart name), "RA=" (image pixel dimensions), "GD=" (horizontal datum), "PR=" (projection), "RGB/" colour palette definitions, and "REF/" lines defining ground control points. The BSB file may reference multiple KAP panels, classifying them as base, inset or extension to form a tiled or segmented navigational chart. Version 3.x (e.g. 3.0, 3.07) is commonly used.

Technical identification: files typically begin with a header signature including "VER/" and "BSB/NA=" strings, and often references to "BASE", "KAP" panels. The text header ends with a control-Z (byte value 0x1A) followed by a NUL (0x00) byte; after that comes scan-line run-length-encoded raster image data and an index of strip offsets to allow efficient access.

How to open BSB files

Important: Different programs may use files with the BSB file extension for different purposes, so unless you are sure which format your BSB file is, you may need to try a few different programs.

While we have not verified the apps ourselves yet, our users have suggested five different BSB openers which you will find listed below.

Last updated: August 25, 2026

Various apps that use files with this extension

These apps are known to open certain types of BSB files. Remember, different programs may use BSB files for different purposes, so you may need to try out a few of them to be able to open your specific file.

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