Tools & Resources¶

A curated list of tools, documentation, and libraries for working with Garmin IMG files.

Tools¶

Map Creation¶

Tool	Type	Description
mkgmap	CLI (Java)	Converts OpenStreetMap data to Garmin vector IMG. The definitive open-source vector IMG writer.
cGPSmapper	CLI	Compiles Polish (.mp) format files to Garmin vector IMG. Freeware for personal use.
GPSMapEdit	GUI	Commercial map editor. Exports to cGPSmapper format (.mp).
splitter	CLI (Java)	Splits large OSM datasets into tiles for mkgmap.

Map Inspection¶

Tool	Type	Description
GMapTool	GUI/CLI	IMG file inspection, splitting, and merging. The primary tool for analyzing IMG structure.
GPXSee	Desktop (C++/Qt)	GPS data viewer with full Garmin IMG parser. Useful reference for understanding how devices parse raster data.
cartoload analyze	CLI	Built-in IMG inspection and comparison. See Analyze IMG files.

Tile Download¶

Tool	Type	Description
Mobile Atlas Creator (MOBAC)	GUI (Java)	Downloads map tiles from online sources. Exports to Garmin Custom Maps (KMZ), not IMG directly.

Format Documentation¶

There is no official public specification for the Garmin IMG format. All documentation is reverse-engineered.

Comprehensive Specifications¶

Document	Author	Coverage
Garmin IMG Format (PDF)	Herbert Oppmann	Authoritative reverse-engineered spec for container and subfile formats. The most up-to-date reference.
IMG Format Specification 1.0	John Mechalas (2005)	The most comprehensive vector IMG specification. Complete header fields, FAT structure, subfile formats.
Exploring Garmin's IMG Format	N. Willink (2015)	Practical guide to parsing vector IMG internals. Corrects several errors in the Mechalas spec.

Community Resources¶

QMapShack Wiki — Raster IMG Format — The most comprehensive community documentation for raster-specific IMG format. Complete TRE header layout for raster maps, RGN Type E0 records, LBL28/LBL29 structure.
OSM Wiki — OSM Map On Garmin — Garmin map creation workflows and mkgmap tutorials.

Reference Implementations¶

Project	Language	Description
mkgmap	Java	Reference implementation for IMG writing. Key packages: `imgfmt`, `building`.
GPXSee	C++/Qt	Reference IMG parser. Key files: `src/map/IMG/rgnfile.cpp`, `trefile.cpp`, `lblfile.cpp`.

Device Compatibility¶

Device type	Raster IMG	Vector IMG	JNX (BirdsEye)	KMZ (Custom Maps)
Fenix watches (6+)	Yes	Yes	No	No
Handheld GPS (GPSMap, Montana, Oregon)	Yes	Yes	Yes	Yes (100 tile limit)
Automotive (Drive, DriveSmart)	Limited	Yes	No	No

Alternative Raster Formats¶

JNX (BirdsEye)¶

Simpler raster format with JPEG tiles and metadata. Better documented than raster IMG. Supported on handheld GPS devices but not on Garmin watches.

KMZ (Garmin Custom Maps)¶

ZIP archive with JPEG tiles + KML metadata. Simple to create. Limited to 100 tiles per file. Not suitable for large-scale maps.

Key Differences: Raster vs Vector IMG¶

	Raster	Vector
Content	Pre-rendered JPEG tile imagery	Points, polylines, polygons
Rendering	Device displays JPEG images	Device renders from geometry data
Search/routing	Limited or none	Full address search, turn-by-turn routing
Tool support	Very limited (no open-source writer existed before cartoload)	Extensive (mkgmap, cGPSmapper)
File size	Large (imagery)	Compact

Garmin's professional maps can combine both raster and vector data in a single IMG file — raster background imagery with vector overlays for roads, POIs, and labels.