Countries and borders

A country has people who live there.

It has land with edges called borders. It has leaders who make the rules. And it works together with other countries.

What turns a piece of land into a country? An agreement signed in Montevideo, Uruguay, in 1933 listed four things a country, or state, should have: people who live there for good, a territory with borders, a government, and the ability to make agreements with other countries.

In 1945, 51 countries started the United Nations. By 2011 it had 193 members, after South Sudan joined.

The Montevideo Convention on the Rights and Duties of States, signed on December 26, 1933, says a state should possess a permanent population, a defined territory, a government and the capacity to enter into relations with other states. Its Article 3 adds that a state's political existence is independent of recognition by other states.

There is no single official count of the world's countries, because lists use different rules. The United Nations had 51 original members in 1945 and 193 by 2011, when South Sudan joined; non-member states can also take part as permanent observers, as Switzerland did until it became a member in 2002. Natural Earth, a free world map dataset, counts 258 "countries" in its main file because it lists places such as Greenland separately from the states they belong to.

A border is a line between two countries.

People decide where it goes. Some borders follow rivers. Some follow the tops of mountains. Most borders are lines you cannot see.

A border, or boundary, is a line that separates places run by different governments. People create borders, usually by making agreements called treaties. Some borders follow nature: the border between France and Spain runs along the peaks of the Pyrenees Mountains, and the Rio Grande forms a large part of the border between Mexico and the United States.

Rivers are very common borders. A study by geographers Laurence Smith and Sarah Popelka found that rivers make up 23 percent of the world's international borders, almost one in four. But most borders cannot be seen at all when you stand on them.

National Geographic Education describes political boundaries as lines created by people to separate areas governed by different groups. A physical boundary is a natural barrier, such as a river, mountain range, ocean or desert, and political boundaries often form along them: the France-Spain border follows the crest of the Pyrenees, and the Rio Grande forms much of the Mexico-United States border.

In a database published in 2020, Laurence Smith and Sarah Popelka found that rivers make up 23 percent of international borders, 17 percent of state and provincial borders and 12 percent of county-level borders, as NASA's Earth Observatory reported. Rivers make convenient lines, but they move. A series of earthquakes in 1811 and 1812 shifted the course of the Mississippi River, and together with imprecise early surveys it left a piece of Kentucky, the Kentucky Bend, surrounded by parts of Missouri and Tennessee.

Some borders have markers on the ground.

Between Canada and the United States, workers cut a long, thin path through the forest. Little white markers show where the line is.

The border between Canada and the United States is 8,891 kilometers long. In forests, you can spot it: it looks like a cleared strip about 6 meters wide stretching from horizon to horizon, dotted with white markers.

A team from both countries, the International Boundary Commission, looks after it. It was set up by a treaty in 1908. Its workers cut back trees and bushes, repair old markers and add new ones, so everyone knows exactly where the line is.

Agreeing on a border in a treaty is only the first step; it then has to be marked and maintained. The Canada-United States boundary, 8,891 km (5,525 miles) long, is shown on 256 official boundary maps. The International Boundary Commission, founded under the Treaty of 1908 to re-establish and map the line from the Atlantic to the Pacific, inspects, maintains and re-establishes more than 8,000 monuments and reference points.

Through forest, the commission keeps a cleared swath called a vista, 3 meters on each side of the line, about 6 meters in all; recleaning its 2,172 km of forest and brush is a major part of the work. The commission says its surveys do not redefine the boundary: the monuments as set on the ground define it, and new surveys improve the record of where they are. It also controls all work done within the vista.

Borders do not stay the same forever.

Sometimes countries buy or swap land. Sometimes a new country is born. Then mapmakers draw new maps.

Borders change over time. National Geographic Education explains that they can change through wars, treaties and trade. In 1803, the United States bought a huge area of land from France, called the Louisiana Purchase, and its western border moved far across the continent.

New countries appear too. In 2011, South Sudan became a separate country from Sudan, and it joined the United Nations the same year. Every change means that maps, globes and school atlases have to be updated.

Political boundaries change through wars, treaties and trade. In the Louisiana Purchase of 1803, the United States bought about 2,147,000 km² from France, and its western boundary moved from the Mississippi River to around what is now Yellowstone National Park. After World War II, much of the map of Europe was redrawn.

Countries also divide and merge. Czechoslovakia was an original UN member; it ceased to exist at the end of 1992, and the Czech Republic and Slovakia were admitted separately in 1993. South Sudan voted to become independent from Sudan and became the 193rd UN member in 2011. Because borders change, a map is always a picture of one moment.

Maps show borders as lines.

Each country is often a different color. In a few places, people do not agree where a line should go. Mapmakers have to choose how to show those places.

On a political map, borders are drawn as lines and countries are often given different colors. Borders can reach out to sea too: the United States, for example, has a territorial sea that goes 12 nautical miles out from its coast.

In some places, governments do not agree about where a border should be or who should run an area. These are called disputed areas. Mapmakers must choose how to draw them. Natural Earth, a free world map, draws borders where control is on the ground and keeps the disputed areas in a separate layer, so map users can see them.

Maps simplify borders into lines, but a border's legal status can be complicated. Borders reach out to sea as well. NOAA describes the United States' 12-nautical-mile territorial sea and an exclusive economic zone (EEZ) reaching no more than 200 nautical miles, within which it has rights over natural resources.

Some borders and some areas are disputed, which means that two or more governments disagree about them. Mapmakers handle this in different ways. Natural Earth shows de facto boundaries, according to who controls a territory on the ground, rather than de jure (legal) claims; it publishes a separate layer of breakaway and disputed areas and optional versions drawn from the point of view of particular countries. A careful map reader checks whose rules a map follows.