4.5 The Function of Political Boundaries

Before a boundary works as a real limit on a state's sovereignty, it usually goes through four steps.

• Defined: described in a legal document, usually a treaty, often in words or coordinates.
• Delimited: drawn on a map by surveyors and cartographers.
• Demarcated: marked on the ground with physical objects like fences, walls, pillars, signs or buoys. Many boundaries are never fully demarcated.
• Administered: managed and enforced over time by the state, through border guards, customs checks, passports and visas.

Disputes can arise at any step. Geographers often group them into four kinds: definitional (arguing over a treaty's wording), locational (arguing over where the line actually runs, for example when a river shifts), operational (arguing over how the border works, such as migration or smuggling), and allocational (arguing over resources that cross the line, like an oil field or a river's water).

Borders frequently line up with differences in culture, national identity or wealth. The U.S.–Mexico border separates countries with very different average incomes. On the island of Hispaniola, the border between French- and Creole-speaking Haiti and Spanish-speaking Dominican Republic is visible from space in places, because there is more forest on the Dominican side.

Some boundaries come from military ceasefires. The Korean Demilitarized Zone (DMZ), set by the 1953 armistice, is a strip about 4 kilometers (2.5 miles) wide and about 250 kilometers (160 miles) long that separates North and South Korea. A UN buffer zone has divided Cyprus since 1974.

Others come from policy decisions. At the Berlin Conference of 1884–85, European powers, along with the United States and the Ottoman Empire, set rules for claiming African territory, with no African representatives present. It required that new claims, at least along the coast, be backed by effective control on the ground, recognized King Leopold II of Belgium's claim to the Congo, and sped up the Scramble for Africa. Most African borders were drawn later in separate agreements between colonial powers.

Agreements can also open borders. In the Schengen Area, which includes most EU countries and a few others, people can usually cross national borders without passport checks.

The United Nations Convention on the Law of the Sea (UNCLOS) was signed in 1982 and took effect in 1994. It spells out what a coastal country may control offshore and what stays open to every country. The United States hasn't ratified it but follows most of its rules. Distances are measured from a coastal baseline in nautical miles; one nautical mile is 1.852 km.

EEZs give even tiny island states huge ocean areas, so islands and reefs can be very valuable. When EEZs overlap, countries must negotiate, often splitting the difference with a median line. Disputes over islands and resources in the South China Sea, the East China Sea and the Arctic show how maritime boundaries can encourage cooperation or cause conflict.