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.
Physical 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.
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
Political boundaries are the dividing lines between countries, states, provinces, counties, and cities. These lines, more often called borders, are created by people to separate areas governed by different groups. Sometimes, political boundaries follow physical boundaries, but most of the time you can’t see them. Most maps show political boundaries. Political boundaries change over time through wars, treaties, and trade. After World War II, the map of Europe was almost completely redrawn. Germany’s eastern border was moved farther west, and the country itself was later divided into East and West Germany. In 1803, the United States bought 2,147,000 square kilometers (828,800 square miles) of land in a treaty with France. This land, the Louisiana Purchase, expanded the size of the U.S. to include the areas that are now Arkansas, Missouri, Iowa, Oklahoma, Kansas, Nebraska, and parts of Minnesota, North and South Dakota, New Mexico, Montana, Wyoming, Colorado, and Louisiana. The western boundary of the U.S. moved from the Mississippi River to what is now Yellowstone National Park.An important type of political boundary in the United States is the boundary of a congressional district. A congressional district is an area that elects a representative to the U.S. House of Representatives. After the U.S. Census, which is taken every 10 years, the population of a state may grow or shrink enough to gain or lose a representative in the House. When this happens, congressional district lines are redrawn in a complicated and controversial process called redistricting. The boundaries between congressional districts may unite or divide economic, social, or ethnic neighborhoods. Political boundaries are just one type of artificial, or man-made, boundary. Other boundaries created by people include linguistic, economic, and social boundaries. Linguistic boundaries form between areas where people speak different languages. Often, these boundaries match political boundaries. For example, the predominant language in France is French, and the predominant language in Germany is German. In India, 122 different languages are spoken by more than 10,000 people each. The Indian
