Topographic map of France: the IGN map, explained

What is the IGN map?

IGN stands for Institut national de l'information géographique et forestière. It was founded in 1940 to take over from the army's geographic service, and it has surveyed and mapped the whole of France ever since. When a French guidebook says "carte IGN", it means the official topographic map: the one with the contour lines, the refuges, the footpaths and the names of every col and torrent.

Most people know it as a folded paper sheet. The famous one is the TOP 25, drawn at 1:25 000, where 4 cm on paper is 1 km on the ground. It is the standard map for walking, ski touring and mountaineering in France, and it is the map mountain rescue and refuge wardens will assume you are carrying.

The same survey data also feeds a digital map called Plan IGN. It is what you see on this page: one seamless map of the country that redraws itself as you zoom, from the whole of France down to individual buildings and paths.

How the map is made, and which IGN map is which

IGN keeps a national geographic database built from aerial photography, LiDAR and field surveys. Roads, buildings, rivers, forest edges, contour lines and place names all live there as data. Plan IGN is drawn from that database by software, at a series of zoom levels, and is refreshed as the database changes rather than sheet by sheet.

That makes it different from the paper family, which is compiled and printed as editions. The names get confusing quickly, so here is the family in one table.

• Plan IGN (Multi-scale, digital): The seamless digital map, open licence since IGN made its public data free in 2021. This is the map shown on this page and in Traverse.
• TOP 25 / Série Bleue (1:25 000): The paper hiking sheets. 10 m contours in the mountains, marked trails overprinted, tourist information, a GPS-compatible grid. Its scanned version, SCAN 25, is a separately licensed product and is not part of the open data.
• TOP 100 (1:100 000): Regional touring sheets for cycling and driving. Good for an overview, too coarse for mountain navigation.
• Carte de 1950 (1:50 000): Scans of the 1:50 000 sheets published around 1950. A snapshot of the country before ski resorts, reservoirs and seventy years of glacier retreat. Switch to it in the map on this page.

How to read the IGN map

The symbols below are the ones that matter in the mountains. Each one has a button that moves the live map to a place where you can see it for real.

• Brown contour lines: Each line joins points of equal height. Lines close together mean steep ground, lines far apart mean gentle ground. Every few lines a thicker index contour carries its elevation in metres. Count the lines between two labelled ones to get the interval at your zoom level.
• Blue contours on white: On glaciers and permanent snow the contours turn blue and the ground is left white. If your route crosses blue contours, you are on ice: rope, crampons and crevasse rescue skills apply.
• Short blue dashes on a glacier: Crevasse zones. They show where the ice is known to break up, usually on steepening ground and the outside of bends. They are a drawing of a pattern, not a survey of individual crevasses, and glaciers change every season.
• Grey contours and rock drawing: Cliffs, rock faces and ridges are drawn in grey. Tightly stacked grey lines mean a wall. A path that crosses them is likely to be a scramble, a via ferrata or a climb.
• Green areas: Forest. The upper edge of the green is the treeline, a quick way to judge where shelter ends and where a ski descent turns into tree skiing.
• Pale tan areas with shading: Open ground above the trees: pasture, scree and moraine. The grey shading is hillshade, lit from the north-west, which makes ridges and valleys readable at a glance.
• Blue lines, solid and dashed: Streams and rivers. A dashed blue line is an intermittent stream, one that may be dry in late summer. Do not plan your water around it.
• Thin black dashed lines: Footpaths. A solid thin line is a track wide enough for a vehicle. The digital Plan IGN does not overprint the GR long-distance trails the way the paper TOP 25 does, so bring your route as a GPX or draw it on top.
• Green house symbol: A refuge or mountain hut. "Refuge" usually means a wardened hut in season. "Cabane" and "abri" mean a simple unwardened shelter.
• Straight lines with end stations: Cable cars, gondolas and chairlifts. Useful for planning an approach, and a reminder that you are inside or next to a ski area.

1. Start with the shape: Zoom out until you can see the whole valley and read the hillshade first: where the ridges run, which side the glacier drains, where the cols are.
2. Then read the steepness: Zoom in until contours appear and look at their spacing along your line. Evenly spaced and wide is a walk. Bunched together is steep. Merged into grey rock drawing is a wall.
3. Check every height: Summits, cols and lakes carry spot heights in metres. Subtract the start from the high point and you have your ascent before you have opened any other tool.
4. Translate the names: French maps describe the terrain in the place names themselves. Aiguille is a needle-like peak, combe is a hanging valley, brèche is a notch in a ridge. The glossary below covers the ones you will meet.

Browse the live Plan IGN map

This page loads the real IGN France tiles in an interactive map, with Plan IGN and 1950 edition and shortcuts to Mer de Glace (Mont Blanc massif), Chamonix valley (Haute-Savoie), La Meije (Écrins), Cirque de Gavarnie (Pyrenees), Monte Cinto (Corsica), Calanques (Marseille coast).

French map words, in English

Place names on the IGN map are descriptions. Knowing a few dozen words tells you what the terrain looks like before you get there.

Aiguille

Sharp, needle-like peak

Arête

Narrow ridge

Brèche

Notch or gap in a ridge

Col / Pas

Pass

Combe

Small high valley or bowl

Crête

Ridge crest

Dôme

Rounded, often snowy summit

Glacier

Glacier

Lac

Lake

Mont / Pic / Tête

Mountain / peak / head-shaped summit

Moraine

Ridge of glacial debris

Névé

Permanent snow patch

Pierrier / Éboulis

Scree

Torrent / Ruisseau

Mountain stream / brook

Cascade

Waterfall

Source / Fontaine

Spring / fountain

Refuge

Mountain hut, usually wardened in season

Cabane / Abri

Basic unwardened shelter

Gîte d'étape

Walkers' hostel

Chalet / Alpage

Mountain farm building / summer pasture

Sentier

Footpath

Passerelle

Footbridge

Téléphérique / Télésiège

Cable car / chairlift

Forêt / Bois

Forest / wood

The 1950 map: the same mountains, seventy years earlier

IGN has scanned the 1:50 000 sheets it published around 1950 and made them available as a single layer. They are drawn by hand: brown contours, blue glacier contours, dotted moraines, and a purple kilometre grid across every sheet.

The most useful thing to do with it is compare. Switch the map on this page to the 1950 edition over the Mer de Glace and look at where the ice ends and how high it sits against the valley walls. Then switch back. The long run of ladders and steps that now leads down from Montenvers to the glacier exists because the ice surface lies far below where that sheet shows it.

It is also a record of old paths, abandoned hamlets and the valleys that were later flooded for hydro-electric reservoirs, which makes it a good companion for anyone researching an old route description.

What the map does not tell you

• It shows the ground, not the conditions. Snow cover, avalanche danger, a washed-out bridge or a closed refuge are not on any topographic map.
• Glaciers move faster than maps. Outlines and crevasse zones are a survey of one moment. Treat them as a starting point and look at recent imagery and reports.
• A path on the map is not a promise. High paths get rerouted after rockfall, and a dashed line across steep ground may be exposed or seasonal.
• Steepness is implied, not measured. Reading slope angle from contour spacing takes practice, which is why a slope-angle overlay is worth having next to the contours.

Use the IGN map in Traverse

Traverse is a mountain mapping app for the web and iPhone. Plan IGN and the 1950 edition are both in it, drawn on real 3D terrain, alongside the layers a paper map cannot give you.

• The IGN map in 3D: The same cartography draped over the terrain, so a wall of tight contours looks like the wall it is.
• Slope angle on top: Shade everything over 30° across the IGN map to see avalanche terrain and the low-angle way around it.
• Recent snow and glacier context: SnowSight shows satellite-observed snow cover with its date. GlacierIQ adds glacier outlines, ice flow and a crevasse-susceptibility index.
• Routes, GPX and offline: Draw a route or import a GPX, get distance, ascent and a profile, then download the area for use without signal.

A Traverse account is free and includes the Traverse, Summer, Winter and Satellite maps with slope angle and aspect. Official national maps, including both IGN maps, are part of Traverse Pro.

Create a free Traverse account · Download Traverse for iPhone

Frequently asked questions

Is the IGN map of France free?

The digital Plan IGN is. Since 1 January 2021 IGN publishes most of its public data, Plan IGN included, under an open licence. The scanned 1:25 000 hiking map (SCAN 25) and the paper TOP 25 sheets are still separate paid products. You can browse Plan IGN for free on this page.

What is the difference between Plan IGN and the TOP 25?

The TOP 25 is a paper map at a fixed scale of 1:25 000, compiled by cartographers, with marked trails and tourist information overprinted. Plan IGN is a digital map generated from the same national database, which redraws at every zoom level. The terrain, contours, paths and names agree. The TOP 25 adds the hiking overprint, and Plan IGN adds zoom and national coverage in one piece.

What scale is the IGN hiking map?

1:25 000. One centimetre on the map is 250 metres on the ground, so 4 cm is 1 km. Contours are every 10 metres in mountain areas and every 5 metres in flatter country.

Are heights on IGN maps in metres or feet?

Metres above sea level, measured against the French national height datum (NGF), which is tied to the tide gauge in Marseille for the mainland and to Ajaccio for Corsica.

Does the IGN map cover the whole Alps or Pyrenees?

It covers French territory. The map stops at the border, so for the Swiss and Italian sides of the Mont Blanc massif or the Spanish Pyrenees you need the neighbouring national maps. Traverse includes swisstopo and the Spanish IGN map for that reason.

Can I use the IGN map offline?

A paper TOP 25 needs no battery, and it is still worth carrying. For a phone, you need an app that can download the tiles before you leave. Traverse lets you save a region of the IGN map, with your route and terrain layers, for use without signal.

How do I see how a glacier has changed on the IGN map?

Compare the current Plan IGN with the 1950 edition. On this page, open the Mer de Glace, switch between the two editions and look at the position of the glacier tongue and the height of the ice against the valley sides.

Sources

• IGN, Institut national de l'information géographique et forestière
• Plan IGN in the national geodata catalogue
• SCAN 25 in the national geodata catalogue
• Remonter le temps, IGN's historic map and photo viewer
• Licence Ouverte / Open Licence 2.0 (Etalab)