New American Standard Bible (©1995)
and He made from one man every nation of mankind to live on all the face of the earth, having determined their appointed times and the boundaries of their habitation,(Acts 17:26)
A boundary is a real or imaginary line that separates two things. In geography, boundaries separate different regions of the Earth. There are many different types of boundaries.
The most obvious type of boundary is a physical boundary. A physical boundary is a naturally occurring barrier between two areas. Rivers, mountain ranges, oceans, and deserts can all serve as physical boundaries. Many times, political boundaries between countries or states form along physical boundaries. For example, the boundary between France and Spain follows the peaks of the Pyrenees mountains, while the Alps separate France from Italy.
The Strait of Gibraltar is the boundary between southwestern Europe and northwestern Africa. This narrow waterway between the Atlantic Ocean and the Mediterranean Sea is an important political, economic, and social boundary between the continents.
Rivers are common boundaries between nations, states, and smaller political units such as counties. The Rio Grande forms a large part of the boundary between Mexico and the United States. The Mississippi River is the defining boundary between many of the states it winds through, including Iowa and Illinois, Arkansas and Tennessee, and Louisiana and Mississippi.
Borders define geographic boundaries of political entities or legal jurisdictions, such as governments, sovereign states, federated states and other subnational entities. Some borders—such as a state's internal administrative borders, or inter-state borders within the Schengen Area—are open and completely unguarded. Other borders are partially or fully controlled, and may be crossed legally only at designated border checkpoints and border zones may be controlled. Some, mostly contentious, borders may even foster the setting up of buffer zones.
Another type of physical boundary lies below the Earth’s surface. The Earth’s shell, or crust, is made of thick slabs of rock called tectonic plates. There are seven major tectonic plates and many smaller ones. These plates are constantly moving.
Interaction between tectonic plates creates activity on their boundaries. Sometimes, the plates spread apart from each other, creating ocean trenches and, eventually, continents. This is called a divergent boundary. Sometimes one plate slides underneath the other, creating volcanoes and earthquakes. This is called a convergent plate boundary. Sometimes the plates grind past each other, creating earthquake fault lines. This is called a transform fault or transform boundary.
The movement between the massive Pacific plate and the plates that border it creates all three types of boundaries. This tectonically active area is called the Ring of Fire. The divergent boundary between the Cocos and Nazca plates creates the Galapagos Ridge, off the coast of South America. The convergent boundary between the Pacific and Australian plates makes the island nation New Zealand very volcanically active. The transform fault between the Pacific and North American plates makes the U.S. state of California prone to earthquakes.