How borders get drawn

Look at a world map for long enough and the borders start sorting themselves into kinds. Some wander; some run dead straight for hundreds of kilometres. Some follow a river or a mountain crest; others cut across both without acknowledgement. The difference is rarely aesthetic. It usually tells you who drew the line and how much they knew about the ground.

Borders that grew

Most European borders are what geographers call subsequent boundaries: they were settled after the population was already there, and they wander because they follow something real — a language boundary, an old duchy, the result of a particular war.

The Portugal–Spain border is the extreme case of stability, largely fixed since the Treaty of Alcañices in 1297 and among the oldest continuously recognised borders in the world. Its irregularity is the evidence of its age: seven centuries of local settlement, each bend recording something.

Borders that were imposed

Straight lines are the signature of a boundary drawn at a distance, usually on a map rather than on the ground, and usually before the drawers had surveyed what was there. Geographers call these superimposed boundaries.

Africa is the obvious case. The Berlin Conference of 1884–85 did not carve up the continent single-handedly — that is a common simplification — but it did formalise the rules by which European powers claimed territory, and the borders that resulted were largely negotiated in Europe. The results are visible: look at the Egypt–Libya–Sudan corner, or Mali's northern edge, and you are looking at lines of latitude and longitude.

North America has its own. The United States–Canada border follows the 49th parallel for roughly 2,000 kilometres, agreed in 1818 and extended west in 1846. It is the longest straight-ish international border in the world, and it too was drawn by negotiators a long way from the prairie.

The most consequential single act of border-drawing in the twentieth century was probably the Radcliffe Line of 1947, which divided India and Pakistan. Cyril Radcliffe, a British lawyer with no prior experience of the subcontinent, was given about five weeks. The line displaced many millions of people and its consequences are still being worked through.

Borders that follow water

Rivers look like ideal boundaries: visible, unambiguous, already there. They are also the least stable option available, because rivers move.

The Rio Grande between the United States and Mexico shifted enough over a century to create the Chamizal dispute, an argument over several hundred hectares near El Paso that took from the 1860s until 1963 to settle. The general fix is legal rather than physical: treaties now usually fix the boundary at the river's position on a particular date, so that the border stays put when the water does not.

Rivers also make poor dividers in a more basic sense. A river valley is typically a single community — the people on both banks trade with each other and are often the same people. A border along a river therefore tends to cut through a population rather than between two.

Borders that follow high ground

Watersheds are more stable. The Chile–Argentina border runs roughly along the Andean crest for more than 5,000 kilometres, the third longest international border in the world, and mountains have the useful property of staying where they are.

They are not free of ambiguity either. "The highest peaks" and "the line dividing the waters" are different lines in places, which is precisely what the two countries argued about for much of the twentieth century.

Borders that stopped meaning anything

A relict boundary is one that no longer has legal force but is still visible in the landscape or the data — the old inner-German border still shows up in forest patterns and election maps decades after it ceased to exist. Cyprus has an active version: the Green Line has divided the island since 1974 without ever becoming an international border.

The borders that are not on land at all

Most of the world's boundary length is maritime, and it is drawn by formula rather than by negotiation. The UN Convention on the Law of the Sea gives a coastal state a territorial sea of 12 nautical miles, where it is essentially sovereign, and an exclusive economic zone reaching 200 nautical miles, where it controls fishing and seabed resources but not navigation.

The consequences are counter-intuitive. Because an EEZ is generated by any piece of land, however small, a scattering of tiny islands produces an enormous maritime territory. France has the largest EEZ of any country — larger than its land area many times over — almost entirely because of small Pacific and Indian Ocean holdings. The United States is second for the same reason.

It also explains why uninhabitable rocks are worth arguing over. A reef that generates 200 nautical miles of fishing and drilling rights in every direction is not a rock, economically speaking, which is the entire substance of several disputes in the South China Sea.

The borders that are frozen by treaty

Antarctica is the one place where border-drawing was deliberately stopped. Seven countries had made territorial claims, several of them overlapping, when the Antarctic Treaty came into force in 1961. Rather than resolving them, the treaty suspended them: existing claims are neither recognised nor renounced, and no new ones may be made.

The result is the only continent with lines on some maps and no borders in practice — which is why Antarctica has no countries on any list, including this site's.

Why the type matters

There is a well-known and much-debated argument in political geography that superimposed borders correlate with later instability, because a line drawn without reference to who lives where is more likely to split one group across two states or force two into one. The correlation is easier to demonstrate than the mechanism, and plenty of straight-line borders are entirely peaceful. But it is a reasonable first guess at why some regions inherited harder problems than others.

None of this is visible from a list of country names, which is the argument for learning borders as relationships rather than as facts. The border quiz asks who neighbours whom; the map quiz puts the shapes in front of you. Both teach the thing a list cannot.