Physical Boundaries

Important physical features on Earth’s surface can make good boundaries because they are easily seen, both on a map and on the ground. Three types of physical elements serve as boundaries between states: deserts, mountains, and water.

Desert Boundaries

A boundary drawn in a desert can effectively divide two states because deserts are hard to cross and sparsely inhabited. Desert boundaries are common in Africa and Asia. In North Africa, the Sahara has in most cases proved to be a stable physical boundary (as well as geometric) separating Algeria, Libya, and Egypt on the north from Mauritania, Mali, Niger, Chad, and the Sudan on the south. Desert borders also are found in South America.

Desert Boundary

Bolivia-Chile border.

Mountain Boundaries

Mountains can be effective boundaries if they are difficult to cross (Figure 8-56). Contact between nationalities living on opposite sides may be limited or completely impossible if passes are closed by winter storms. Mountains are also useful boundaries because they are rather permanent and are usually sparsely inhabited.

Mountain Boundary

Argentina-Chile border.

Mountains do not always provide for the amicable separation of neighbors. Argentina and Chile agreed to be divided by the crest of the Andes Mountains but could not decide on the precise location of the crest. Was the crest a jagged line, connecting mountain peak to mountain peak? Or was it a curving line following the continental divide (the continuous ridge that divides rainfall and snowmelt between flow toward the Atlantic or Pacific)? The two countries almost fought a war over the boundary line. But with the help of U.S. mediators, they finally decided on the line connecting adjacent mountain peaks.

Water Boundaries

Rivers, lakes, and oceans are the physical features most commonly used as boundaries (Figure 8-57). Water boundaries are readily visible on maps and aerial imagery. Historically, water boundaries offered good protection against attack from another state because an invading state had to transport its troops by air or ship and secure a landing spot in the country being attacked. The state being invaded could concentrate its defense at the landing point.

Water Boundaries

Rivers, lakes, and oceans are the physical features most commonly used as boundaries. Water boundaries are readily visible on maps and aerial imagery. In Europe, the Danube and Rhine rivers serve as boundaries between several countries.

Water boundaries are especially common in East Africa: The boundary between the Democratic Republic of Congo and Uganda runs through Lake Albert. The boundary separating Kenya, Tanzania, and Uganda runs through Lake Victoria. The boundary separating Burundi, the Democratic Republic of Congo, Tanzania, and Zambia runs through Lake Tanganyika. The boundary between Malawi and Mozambique runs through Lake Nyasa, which is also known as Lake Malawi.

Water boundaries may seem to be set permanently, but the precise position of water may change over time. Rivers, in particular, can slowly change their course. The Rio Grande, the river separating the United States and Mexico, has frequently meandered from its previous course since it became part of the boundary in 1848. Land that had once been on the U.S. side of the boundary came to be on the Mexican side and vice versa. The United States and Mexico have concluded treaties that restore land affected by the shifting course of the river to the country in control at the time of the original nineteenth-century delineation. The International Boundary and Water Commission, jointly staffed by the United States and Mexico, oversees the border treaties and settles differences.

The Law of the Sea

The United Nations Convention on the Law of the Sea defines the rights and responsibilities of countries with respect to the use of the world’s oceans and the management of marine resources. It has been signed by 164 states (not including the United States). The Convention identifies three types of water boundaries:

• Territorial waters. Up to 12 nautical miles from shore (about 22 kilometers or 14 land miles), a state may set laws regulating passage by ships registered in other states.

• Contiguous zone. Between 12 and 24 nautical miles from shore, a state may enforce laws concerning pollution, taxation, customs, and immigration.

• Exclusive economic zone. Between 24 and 200 nautical miles, a state has the sole right to the fish and other marine life.

Territorial Ocean Zones Defined by The Law of the SEA

These rules apply except where countries with overlapping claims negotiate compromise boundaries.

The Law of the SEA Applied to Australia and Neighbors

Disputes can be taken to a tribunal for the Law of the Sea or to the International Court of Justice.

Through enforcement of the exclusive economic zone, states bordering an ocean are able to claim vast areas of the ocean for control of valuable resources. This has become especially important in the delineation of boundaries in the polar regions (see Sustainability & Our Environment feature in this chapter).

Pause & Reflect 8.4.2

What examples have you seen thus far in this chapter of physical features that have not served as peaceful boundaries?