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The Project

Free, accurate and up-to-date Garmin topographic maps — forged from IGN open data, with a 100% open-source pipeline.

A declarative YAML becomes a Garmin map

The declarative approach: your symbology rules in YAML, the tool forges the .img.

Why this project?

Garmin hiking GPS devices (fenix, Oregon, eTrex, Montana, Alpha...) use a proprietary map format: the Garmin IMG. To load your own geographic data onto a Garmin GPS, you need to produce a gmapsupp.img file — an opaque binary, not publicly documented, that only a few tools know how to generate.

Historically, the production chain relied on proprietary software (FME, Global Mapper, GPSMapEdit), freeware (cGPSmapper, GMapTool) or the open-source Java tool mkgmap. These tools exist and have helped advance the field — this project does not claim to be a silver bullet, but offers a free and reproducible alternative to this heterogeneous chain.

Known limitations

This project is an evolving personal work. Current limitations: experimental routing (hardcoded, not configurable), no handling of complex restrictions (tonnage, height), coverage limited to IGN BD TOPO data. Contributions and feedback are welcome.

The FOSS approach

This project embodies an end-to-end approach:

  1. Data is open — The IGN BD TOPO is available under the Etalab 2.0 license since January 1, 2021
  2. Tools are open-source — ogr-polishmap under MIT license (GDAL compatibility), mpforge and imgforge under GPL v3 license (copyleft)
  3. The process is reproducible and extensible — One script, one YAML configuration, and anyone can rebuild the map. The pipeline is not limited to BD TOPO: it is sufficient to adapt the YAML files to use other geographic data sources
  4. Zero proprietary dependency — No FME, no Global Mapper, no GPSMapEdit, not even Java

Supported platform

Binaries are currently compiled for Linux x86_64 only. A Windows build is conceivable for imgforge (pure Rust), but remains complex for mpforge (static GDAL linking).

Before / After

Criterion Old pipeline New pipeline
License Proprietary FME + mkgmap (Java) 100% open-source (MIT / GPL v3)
Automation Manual, step by step Full (scripts + CI/CD)
Reproducibility Low (operator-dependent) Total (declarative configuration)
Performance Java, JVM overhead Native binary, parallelized (Rust, rayon)
System dependencies FME, Java JRE, GPSMapEdit Rust, GDAL (or static binary)
Intermediate format Manual editing in GPSMapEdit Polish Map generated automatically

The three pillars of the project

The pipeline rests on three tools developed specifically for this project:

  • ogr-polishmap — The GDAL/OGR Driver

    A C++ driver that teaches GDAL how to read and write the Polish Map format (.mp). It is the founding brick: without it, it is impossible to convert standard GIS data to the intermediate format required by Garmin compilers.

    Learn more

  • mpforge — The Tile Forger

    A Rust CLI that slices massive geospatial data (Shapefile, GeoPackage) into Polish Map tiles, with parallelization, YAML field mapping, and JSON reports for CI/CD integration.

    Learn more

  • imgforge — The Garmin Compiler

    A Rust CLI that compiles Polish Map tiles into a binary Garmin IMG file. It replaces mkgmap with a single dependency-free binary, supporting multi-format encoding, routing, TYP symbology, and DEM/hill shading.

    Learn more

Roadmap

ogr-garminimg — Garmin IMG Driver (coming soon)

A future GDAL/OGR C++ driver to read Garmin IMG files (.img) natively. It will allow opening a gmapsupp.img directly in QGIS, ogr2ogr, or any GDAL tool — making the binary Garmin format finally accessible to the GIS ecosystem. This project is at the design stage.

The data flow

%%{init: {'theme': 'base', 'themeVariables': {'primaryColor': '#4caf50', 'lineColor': '#90a4ae', 'secondaryColor': '#ff9800', 'tertiaryColor': '#2196f3'}}}%%
flowchart LR
    A["BD TOPO IGN<br/>.gpkg / .shp"] --> B["mpforge build<br/>spatial tiling"]
    B --> C["tiles/*.mp<br/>Polish Map"]
    C --> D["imgforge build<br/>compilation"]
    D --> E["gmapsupp.img<br/>Garmin Map"]
    E --> F["Garmin GPS"]

    style A fill:#4caf50,stroke:#2e7d32,color:#fff
    style B fill:#78909c,stroke:#546e7a,color:#fff
    style C fill:#ff9800,stroke:#e65100,color:#fff
    style D fill:#78909c,stroke:#546e7a,color:#fff
    style E fill:#2196f3,stroke:#1565c0,color:#fff
    style F fill:#e91e63,stroke:#c2185b,color:#fff

What the maps contain

A Garmin topographic map of France (or a region) including:

  • Roads and paths — complete road network from the IGN BD TOPO
  • Hydrography — rivers, lakes, wetlands, canals
  • Buildings and urban areas — built-up area footprints
  • Vegetation — forests, hedgerows, orchards, vineyards
  • Relief — contour lines and shading (DEM/hill shading)
  • Toponymy — place names, communes, massifs, summits
  • Routing — turn-by-turn route calculation on GPS (experimental — see warning below)

Experimental routing

The road network is routable on an experimental basis only. Calculated routes are indicative and non-prescriptive — do not rely on them for navigation, regardless of the mode of transport.

The routable network is currently hardcoded based on BD TOPO data attributes. Dynamic configuration based on source routable attributes is not yet supported.

Source data

Maps are generated from the IGN BD TOPO — quarterly updates, metric precision, covering the entire French territory. Open license Etalab 2.0.

Demo

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