Step 1: Downloading Data¶

Source data¶

The IGN BD TOPO is the reference topographic database of the IGN (Institut national de l'information géographique et forestière). It covers the entire French metropolitan and overseas territory.

Optional complementary data¶

Automated download¶

The download-data.sh script automates downloading from the IGN Géoportail:

By department¶

# Download a department (Isère) with all complementary data
./scripts/download-data.sh --zones D038 --with-contours --with-osm --with-dem

# Multiple departments
./scripts/download-data.sh --zones D038,D069 --with-contours --with-osm --with-dem

By region¶

# Auvergne-Rhône-Alpes
./scripts/download-data.sh --region ARA --with-contours --with-osm --with-dem

Full France¶

./scripts/download-data.sh --region FXX --with-contours --with-osm --with-dem

Targeting a specific edition¶

By default, the script downloads the latest edition published by the IGN. Three options allow pinning an earlier edition (useful for reproducing a historical build or waiting for an edition to be fully published):

# 1. List available editions for an area (downloads nothing)
./scripts/download-data.sh --zones D038 --list-editions

# 2. Resolve via API the latest edition for a given month
./scripts/download-data.sh --zones D038 --bdtopo-version v2025.09

# 3. Force an exact edition date
./scripts/download-data.sh --zones D038 --date 2025-09-15

Data organization¶

The script automatically organizes downloaded files:

pipeline/data/
├── bdtopo/
│   └── 2025/
│       └── v2025.12/
│           ├── D038/
│           │   ├── ADMINISTRATIF/
│           │   ├── BATI/
│           │   ├── HYDROGRAPHIE/
│           │   ├── LIEUX_NOMMES/
│           │   ├── OCCUPATION_DU_SOL/
│           │   ├── SERVICES_ET_ACTIVITES/
│           │   ├── TRANSPORT/
│           │   │   ├── TRONCON_DE_ROUTE.shp
│           │   │   ├── TRONCON_DE_VOIE_FERREE.shp
│           │   │   └── ...
│           │   └── ZONES_REGLEMENTEES/
│           └── D069/
│               └── ...  (same structure)
├── contours/
│   ├── D038/
│   │   ├── COURBE_0800_6480.shp
│   │   └── ...
│   └── D069/
├── dem/
│   ├── D038/
│   │   ├── BDALTIV2_25M_*.asc
│   │   └── ...
│   └── D069/
├── osm/
│   ├── auvergne-latest.osm.pbf
│   ├── rhone-alpes-latest.osm.pbf
│   └── gpkg/
│       ├── auvergne-latest-amenity-points.gpkg
│       ├── rhone-alpes-latest-shop-points.gpkg
│       └── ...
└── hiking-trails/
    └── FRANCE-GR.shp

Zone codes¶

Metropolitan regions¶

Departments¶

Codes D001 to D976 (standard department number).

Elevation data (DEM)¶

For hill shading and altitude profiles on the GPS, elevation data is required:

SRTM (NASA) — recommended for beginners¶

# Download SRTM tiles for France
# From http://dwtkns.com/srtm30m/ (NASA registration required)
# Required tiles: approximately N42E000 to N51E010

HGT files are directly usable by imgforge (--dem ./srtm_hgt/).

BDAltiv2 (IGN) — high-resolution France¶

ASC files in ESRI ASCII Grid format (25 m), in Lambert 93 projection, are automatically downloaded by download-data.sh with --with-dem and stored in pipeline/data/dem/{zone}/. imgforge uses them with built-in reprojection (--dem ./pipeline/data/dem/D038/ --dem-source-srs EPSG:2154). For multi-zone, the build-garmin-map.sh script passes one --dem per department.

OSM data (OpenStreetMap)¶

OpenStreetMap data complements BD TOPO with POIs (shops, restaurants, pharmacies...) and natural features (caves, cliffs, viewpoints) not present in IGN data.

Downloading from Geofabrik¶

The download-data.sh script also handles downloading .osm.pbf files from Geofabrik:

# BDTOPO + OSM for Auvergne-Rhône-Alpes
./scripts/download-data.sh --region ARA --with-osm

# Full France (BDTOPO + single OSM file ~4.5 GB)
./scripts/download-data.sh --region FXX --with-osm

# Simulate without downloading
./scripts/download-data.sh --region ARA --with-osm --dry-run

OSM data organization¶

Geofabrik PBF files are automatically converted to GPKG by download-data.sh (--with-osm), which eliminates GDAL OSM driver memory errors on large PBFs.

pipeline/data/osm/
├── auvergne-latest.osm.pbf           ← Source PBF (kept)
├── rhone-alpes-latest.osm.pbf
└── gpkg/                             ← Extracted GPKG (used by mpforge)
    ├── auvergne-latest-amenity-points.gpkg
    ├── auvergne-latest-shop-points.gpkg
    ├── auvergne-latest-natural-lines.gpkg
    ├── auvergne-latest-natural-points.gpkg
    ├── auvergne-latest-tourism-points.gpkg
    └── ...

GPKG files are directly usable by mpforge — no OSM configuration (osmconf.ini) needed for GPKG.

Vector contour lines¶

10 m interval contour lines are available as vector data (Shapefile) from the IGN. They are automatically downloaded by download-data.sh with the --with-contours option and stored in pipeline/data/contours/{zone}/.

inputs:
  # Contour lines — multi-zone via brace expansion
  - path: "${CONTOURS_DATA_ROOT}/{${ZONES}}/**/COURBE_*.shp"
    source_srs: "EPSG:2154"
    target_srs: "EPSG:4326"
    spatial_filter:
      source: "${DATA_ROOT}/{${ZONES}}/ADMINISTRATIF/COMMUNE.shp"
      buffer: 500

The spatial_filter is important for contours: it restricts processing to the communes of the selected zones, avoiding loading unnecessary contour tiles.

Contour lines will then be sliced into Polish Map tiles and compiled into the final Garmin map, independently of the DEM used by imgforge for hill shading.