France's geography: a hexagon with its longest border in South America

Where the French frontier actually runs

France holds 3,966.2 km of land boundary in total, and 2,751 km of that lies in Europe. French Guiana accounts for 1,205 km, and a line of 10.2 km drawn across the island of Saint Martin in the Caribbean accounts for the remainder. The longest single stretch is the 649 km between French Guiana and Brazil, which runs three kilometres longer than the 646 km France shares with Spain along the Pyrenees.

Eleven states have territory touching French territory, and three of them sit outside Europe. Brazil and Suriname border French Guiana. The Kingdom of the Netherlands borders France on Saint Martin, where the northern half of the island is a French overseas collectivity and the southern half is Sint Maarten.

Inside Europe most of the boundary follows relief that predates the treaties drawn along it: the Pyrenees in the south, the Alps and the Jura in the southeast, the Rhine in the east. The northeast is the exception, where the lines with Belgium and Luxembourg cross open plain and were settled by agreement rather than by terrain. Monaco, with 6 km of boundary, is an independent enclave on the Mediterranean coast, and Andorra, with 55 km, lies between France and Spain in the mountains.

Why French waters reach into every ocean

The land border is the smaller half of the problem. France shares maritime delimitations with thirty other states along roughly 22,860 km of common frontier, and the water inside those lines came to 10,911,921 km² in the figures the naval hydrographic service published for 2023, counting the continental shelf extensions in force on 26 January 2023. Without those extensions the same table gives 10,186,624 km². 97% of it is overseas.

French Polynesia alone carries nearly thirteen times the maritime space of metropolitan France. Clipperton, an uninhabited Pacific island administered by the high commissioner of the French Republic in French Polynesia, carries more of it than metropolitan France does. Some 9.5 million km² of the exclusive economic zone sits under more than 1,000 metres of water. The coast that generates all of this runs to about 20,000 km across 26 coastal departments in the hexagon and twelve overseas territories, of which roughly 5,500 km is metropolitan.

The figures are worth reading with their provenance attached, because they move. A French Senate annexe reproducing a June 2013 evaluation of maritime policy put the exclusive economic zone at 10.2 million km² and observed that the figure of 11 million is also cited fairly, since it folds in claims no other state contests; the annexe adds that its own numbers are indicative and rest in places on limits never agreed with the neighbouring state. Two Wikipedia articles give 11,035,000 km² and 11,691,000 km². The spread between all of them is a question of what counts as French water and of when the line was last drawn.

How the hexagon holds its shape

Metropolitan France is roughly hexagonal in outline, which is why the French call it l'Hexagone, and its continental part measures about 1,000 km from north to south and about the same from east to west. It lies between latitudes 41° and 51° N and longitudes 6° W and 10° E, on the western edge of the Eurasian landmass and inside the northern temperate zone. Metropolitan territory covers 551,695 km²; the total with the overseas departments and territories, excluding Adélie Land, is 643,801 km², or 0.45% of the land surface of the planet.

The extreme points show how much the shape depends on which France is being measured. On the European mainland the northernmost point is Bray-Dunes in the Nord at 51°04′ N, the southernmost is Puig de Comanegra at Lamanère in the Pyrénées-Orientales at 42°20′ N, the westernmost is the Pointe de Corsen at Plouarzel in Finistère at 4°47′ W, and the easternmost is Lauterbourg in the Bas-Rhin at 8°13′ E. Add Corsica and the southern and eastern points move to the Îles Lavezzi off Bonifacio and to San-Giuliano near Cervione. Add the overseas departments and the southernmost point becomes Saint-Joseph on Réunion at 21°23′ S. Take the whole republic and it becomes the Îles de Boynes in the Kerguelen at 50°01′ S, with the westernmost at Toloke on Futuna at 178°10′ W.

The hexagon is divided into twelve regions plus the territorial collectivity of Corsica, then into 96 departments, 320 arrondissements, 1,995 cantons and 34,836 communes as counted on 1 January 2021. Five overseas regions, four overseas collectivities, one overseas country, one collectivity of unique status and one overseas territory sit alongside them, each with its own administrative arrangement.

Why the old massifs decide the relief

The frame of the country is a set of worn Palaeozoic highlands arranged in a rough V, thrown up by Hercynian folding between 345 and 225 million years ago. The eastern arm holds the Ardennes, the Vosges and the eastern Massif Central; the western arm holds the western Massif Central and the Massif Armoricain, which is most of Brittany. Their heights are modest, because they have been planed flat and re-exposed repeatedly: the Ballon de Guebwiller tops the Vosges at 1,423 m, and the Mont des Avaloirs tops the Armorican at 417 m.

The Massif Central is the large one, covering about 86,000 km², roughly a sixth of the country. Alpine mountain-building lifted the whole block, steeply on its eastern side and gently under the sediments to the west and north, and the fracturing that came with it opened basins and let magma up. The Puy de Sancy, at 1,885 m, is its summit, and the cinder cones of the Chaîne des Puys west of Clermont-Ferrand formed only about 10,000 years ago and still hold the shape of their craters and lava flows. To the southwest the massif is capped by Jurassic limestone, the causses, dry at the surface, trenched by gorges such as the Tarn, and hollowed by cave systems holding prehistoric painting, at Lascaux in the Vézère valley and at Pech-Merle in the Lot.

Between and around the massifs lie the sedimentary basins, the Paris Basin in the north and the Aquitaine Basin in the southwest, and beyond them the young fold mountains: the Alps, the Pyrenees and the Jura, all far less eroded. Mont Blanc is the high point, published as 4,806 m in the record this catalogue keeps and as 4,810.45 m by Britannica. The low point is the Étang de Lavalduc in the Bouches-du-Rhône, at 10 m below sea level. About 60% of French municipalities carry a moderate seismic risk classification.

One inheritance from the Pleistocene, between about 2,600,000 and 11,700 years ago, matters more than the mountains for what the country grows. France lay outside the great northern ice sheets, so direct glacial sculpting was confined to the Alps, the Pyrenees, the Vosges, Corsica and the highest summits of the Massif Central. Everywhere else went through repeated freezing and thawing, which shifted sheets of shattered rock down the slopes and laid the fine windblown limon that mantles the limestone plateaus and chalk beds of the Paris Basin. Those loess soils are the best arable ground in the country, and they are a periglacial accident rather than a product of the bedrock beneath them.

How the rivers divide the country

A single divide running from the southern Vosges down the eastern and southeastern rim of the Massif Central to the Noire Mountains separates the drainage of France into a large western half and a narrow eastern one. Cols and lowland corridors break it, the Langres Plateau chief among them. Almost every river of the western half rises along that line, and the four main systems, the Seine, the Loire, the Garonne and the Rhône, drain more than 62% of metropolitan territory between them.

The Loire is the longest and the most irregular. It rises on Mount Gerbier-de-Jonc in the Massif Central, runs north over impermeable rock through a series of gorges, turns west inside the Paris Basin, and discharges eight times as much water in December and January as it does in August and September. Its floodplain is laid with sand and gravel, its flow is poor for navigation, and its water cools a chain of nuclear stations along its course. UNESCO listed the valley between Sully-sur-Loire and Chalonnes in 2000.

The Seine, by contrast, keeps a regular flow through the year. It gathers the Yonne, the Marne and the Oise across the Paris Basin, threads the Île de la Cité in the middle of Paris, and reaches the English Channel at Le Havre; reservoirs upstream were built to take the edge off the spring and the autumn peaks. The Garonne is the shortest of the four, rising in the Aran valley on the Spanish side of the Pyrenees and joined by the Tarn, the Lot and the Dordogne out of the Massif Central. It runs low in summer and autumn and ends in the Gironde estuary, which the sea penetrates for about 100 km.

The Rhône is the powerful one. It rises in the Alps, passes through Lake Geneva, takes the Saône at Lyon, and holds an ample flow in every season because Alpine snowmelt peaks in late spring while the Saône and the Mediterranean tributaries peak in autumn and winter. Dams have reworked its course for power and navigation, and it deposits its load into the Camargue from about 40 km inland. Around all of this run 12,261 km of navigable waterway, including the Canal du Midi, which joins the Mediterranean to the Atlantic by way of the Garonne. Lake Bourget, in the Alpine foreland, is the largest natural lake lying entirely within France.

Why the weather changes across the country

Every part of France feels the ocean, moderated by the North Atlantic Drift in the west and the Mediterranean in the south, but the three climates the country is usually divided into behave very differently. Annual mean temperature falls from 15 °C at Nice on the Mediterranean to 10 °C at Lille on the northern border, with Paris at 11 °C in between.

The oceanic climate is purest in Brittany, where Brest averages 6 °C in January and 16 °C in July, takes 890 mm of rain spread through the year, and changes weather several times a day. The continental influence is strongest on the northeastern plains: Strasbourg has the widest temperature range in the country, averages 83 days of frost, and takes its heaviest rain from June and July thunderstorms. Paris sits between the two, on about 58 cm of rain a year with a summer maximum. The Mediterranean south reverses the pattern entirely, with mild winters averaging 8 °C in January at Nice, at least three nearly rainless summer months, sudden autumn downpours, and totals as low as 430 to 500 mm on the Languedoc-Roussillon coast. That same coast takes the mistral, the violent northerly funnelled down towards the Gulf of Genoa.

Altitude overrides all of it. High ground in the west, the western Pyrenees, the Massif Central, the Alps and the Jura takes more than 1,270 mm a year. Snow lies from December to the end of April above 900 m and never leaves above 2,700 m in the Alps or 3,000 m in the Pyrenees. On a valley scale the difference between the sunlit adret slope and the shaded ubac decides where the fields and the houses go.

The recorded extremes span more than 87 degrees. The metropolitan high stands at 46 °C, measured at Vérargues on 28 June 2019; the low at −41.2 °C, measured at Mouthe in January 1985. The hazards that follow from this climate are flooding, hailstorms, avalanches, midwinter windstorms, drought and the summer fires of the Mediterranean south.

What grows and lives on French ground

Almost the whole country falls in the zone of brown forest soils, which develop under deciduous cover in temperate conditions and take farming well. Two things vary that: the limon sheets of the north, which give the finest arable soil, and the decalcified red soils of the Mediterranean fringe.

Forest covers 31% of the land area, an increase of 7% since 1990, and Britannica puts the area at 15,000,000 hectares, more than a quarter of the territory. More than 140 tree species grow in it. Most of it stands on the massifs and in the mountain chains, but the largest single block is planted rather than natural: the maritime pine of the Landes, about 953,000 hectares of sandy plain in the southwest. France scored 4.52 out of 10 on the 2018 Forest Landscape Integrity Index, which measures how heavily worked a forest is rather than how much of it there is.

That coverage is a recovery. The region was open grassland through the Pleistocene, wooded over as the glaciers withdrew from about 10,000 BC, and cleared from Neolithic times onward. The forests were still extensive in the medieval period and largely gone by the 15th century, at which point France bought its timber from Scandinavia and from its North American colonies.

The vegetation splits between a Holarctic province covering most of the country, with oak, chestnut, pine and beech giving way upward to fir, mountain pine and larch, and a smaller Mediterranean province where summer drought favours evergreen oak, cork oak, cistus and lavender. Two forms there are products of clearance as much as of climate: the maquis, dense drought-resistant thicket, and the garrigue, a rock heath over much of the hottest ground in Provence.

The larger fauna is thinned. Red deer, roe deer and wild boar are still hunted; chamois and reintroduced ibex hold the high Alps; the badger, the otter, the beaver, the Alpine marmot and the brown bear and lynx of the Pyrenees are listed as endangered, and seals have almost disappeared from the coasts. Southern France sits at the northern edge of the range of several African migrants, which is why the flamingo, the Egyptian vulture, the black-winged stilt, the bee-eater and the roller breed there and not further north. Nine national parks hold the protected share of all this, alongside the regional nature parks, which the sources count as 46 in one passage and as 54 as of 2019 in another.

Of the land itself, 33.40% was arable and 1.83% under permanent crops as of 2007, with 26,420 km² irrigated in the same year and total renewable water resources of 211 km³ measured in 2011. The minerals are broad and mostly worked out: coal, iron ore, bauxite, zinc, uranium, potash, feldspar, fluorspar, gypsum, gold, clay, petroleum and silver.

Why French cities sit where they do

The Paris Basin is a layered stack of sedimentary rock with the best soils in the country on top of it, drained by an even river, and open in every direction. It is the ground the capital grew on, and what was decided there afterwards belongs to France: history. Paris took shape around an island in the Seine, and the fertility of the loess around it is why the region farms the way it does.

The other cities sit on the passages between the massifs. Lyon holds the junction of the Rhône and the Saône, on the valley the geographers list as a route of natural passage between the north and the Mediterranean. Strasbourg stands where the Ill joins the Rhine, on the Alsace plain of the rift valley below the steep eastern face of the Vosges. Bordeaux commands the Garonne just above the point where the Dordogne joins it to form the Gironde, Nantes and Saint-Nazaire the mouth of the Loire, and Marseille is the largest of the ten major French ports.

Water engineering finished what the terrain started. The Bas Rhône-Languedoc canal, cut after the Second World War for irrigation, made the Languedoc lowland farmable and then urban; the Canal de Provence taps the Durance to supply Aix-en-Provence, Marseille and Toulon with drinking water. Roughly 750 maritime and fluvio-maritime ports work the coast, and 947 communes fall under the Littoral law that governs building along it, 841 of them in metropolitan France and 106 in the overseas departments.

France ended up as a country whose people are concentrated in one temperate hexagon and whose responsibilities are scattered through three oceans. Of the two frontiers France maintains, the one on land is short and settled. The one at sea is nearly six times as long, shared with thirty states, and in places drawn along limits no neighbour has yet agreed.