What is the KAP file format?
.kap files store BSB-format raster nautical charts - digital sea charts developed by Maptech Inc. in the early 1990s. NOAA adopted the format for its official Raster Navigational Charts (RNCs) in 1994, and it became the standard for electronic chart plotters and marine navigation software for over two decades.
Each .kap file consists of two sections. The first is a plain-text ASCII header whose named parameter lines describe the chart: VER/ (format version), BSB/NA= (chart name), RA= (pixel dimensions), GD= (geodetic datum), PR= (projection), RGB/ (indexed color palette, up to 127 entries), REF/ (ground control points), and PLY/ (border polygon). The header ends with a NUL or 0x1A byte. The second section is a binary raster image encoded as scan-line run-length data using a 7-bit palette index system.
GDAL provides read support for .kap via its BSB driver; OpenCPN is the most widely used open-source chart plotter supporting the format. The encrypted BSB v4.0 variant uses the .cap extension and cannot be read by open-source tools. The related .bsb extension is sometimes used alongside .kap in multi-file chart packages.
NOAA officially retired all 1,007 of its RNC .kap charts by December 2024, completing a transition announced in 2019. Modern electronic navigation uses ENC (Electronic Navigational Charts) in S-57/S-101 vector format. .kap files remain in active use for historical navigation, recreational boating software, and GIS research.
Security & safety
RISK: LOWPassive data file (raster chart image + metadata). Contains no executable code. Safe to open. Encrypted .CAP files from BSB v4 will fail to open in standard tools - not a security risk, just DRM.
Format details
in a nutshell- Karaoke text/timing file (KAP) - Some Japanese karaoke systems used .kap for timed lyric scripts - entirely unrelated text format.
Programs that open KAP files
Windows4 apps
MAPC2MAPC
Paid File → Open Map → select .kap; use to convert to other formats (GeoTIFF, OziExplorer etc.). 
Global Mapper
Paid File → Open Data File(s) → select the .kap file; chart renders with georeferencing. 
OpenCPN
Open-source Add the chart folder under Options → Charts → Chart Files; KAP charts display automatically on the chart window. 
macOS1 app
Linux2 apps
GDAL (command line)
Open-source gdal_translate input.kap output.tif - converts BSB to GeoTIFF. gdalinfo input.kap shows metadata. Technical details
deep spec| File structure | Two-part file: ASCII text header + binary raster body, separated by NUL/`0x1A` byte |
| Header format | Named parameter lines: `VER/`, `BSB/NA=`, `RA=`, `GD=`, `PR=`, `RGB/`, `REF/`, `PLY/`, `DTM/`, `DX/DY` |
| Raster encoding | Proprietary scan-line run-length encoding; pixel values are 7-bit palette indices packed as (count, index) pairs |
| Color depth | 7-bit indexed palette - maximum 127 colors defined by `RGB/` entries in the ASCII header |
| Byte order (binary section) | Big-endian |
| Encryption | None in `.kap`; BSB v4.0 encrypted variant uses `.cap` extension (not readable by GDAL or open-source tools) |
| Georeferencing | Ground control points in `REF/` lines; geodetic datum (`GD=`) and projection (`PR=`) declared in header |
| GDAL driver | `BSB` - reads `.kap` and `.bsb`; encrypted `.cap` files not supported |
| Typical file size | 500 KB - 50 MB |
| MIME type | `image/x-kap` |
| Primary distributor | NOAA (Raster Navigational Charts, 1994-2024); 1,007 charts retired by December 2024 |
| Replaced by | ENC (Electronic Navigational Charts) in S-57/S-101 vector format for modern navigation |
| Released | early 1990s (BSB format developed by Maptech for digital nautical charts) |
| Latest version | BSB 4.0 (introduced encryption for CAP files) |
| Open standard | Yes · royalty-free |
| Specification | gdal.org |
KAP conversions
Community Q&A
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