A boundary separates two things. It can be a real or imaginary line. In geography, boundaries separate different regions of the planet. There are many different types of boundaries.

Physical Boundaries

A boundary divides people and places. It can be real or invisible.

A physical boundary happens because of nature. It divides two areas. Rivers, mountains, oceans and, deserts are examples.

Sometimes, physical boundaries also form boundaries between nations or states. For example, the boundary between France and Spain follows the Pyrenees mountains.

Rivers are common boundaries between nations and states, like those in the United States. The Mississippi River is the defining boundary between the Louisiana and Mississippi, for example.

Another type of physical boundary lies below Earth's surface. Earth's shell, or crust, is made of thick slabs of rock called tectonic plates. There are seven major tectonic plates. There are also many smaller ones. These plates are constantly moving.

Sometimes, the plates spread apart from each other. This can break apart continents. Millions of years ago, Africa and Europe were connected. Tectonic plates broke them apart. When these plates move around, they can cause large cracks in the ground, called fault lines. Volcanoes and earthquakes are more likely to happen along fault lines.

There is a fault line near the U.S. state of California. This area is more likely to have earthquakes.

Political Boundaries

Political boundaries are lines dividing up countries, states, counties, and cities. These lines are usually called borders. They are created by people to make areas separate. The areas are governed by different groups.

Sometimes, political boundaries follow physical boundaries. Most of the time you can't see them. Most maps show political boundaries.

Political boundaries change over time through wars, agreements, and trade. After World War II, Germany was divided into East Germany and West Germany.

In 1803, the United States bought a vast area of land from France. This event was called the Louisiana Purchase. It greatly expanded the size of the U.S. The U.S. gained areas we now know as Missouri, Minnesota, New Mexico, North Dakota, South Dakota, and many more.

An important type of political boundary in the United States is the boundary of a congressional district. This is an area that elects a representative to the U.S. House of Representatives. How many representatives a state gets depends on the state's population. If a state gains or loses people over time, that state may gain or lose a representative in the House. When this happens, congressional district lines are redrawn.

Other Boundaries

Other boundaries can be created by people. They are also invisible, but very much felt.

Language boundaries form between areas where people speak different languages. Often, these boundaries match political boundaries. For example, the most common language in France is French. The most common language in Spain is Spanish. Not being able to speak a neighboring region's language can cause tensions between people.

Economic boundaries divide groups by how much money each has. Sometimes these boundaries happen along borders between countries. One example is the border between the United States and Mexico. The U.S. is much richer than Mexico.

Sometimes, economic boundaries can happen within a single city. For example, the Upper West Side is a wealthy neighborhood in the U.S. city of New York, New York. It has good colleges and hospitals. Melrose, just a few kilometers (miles) away, is a poorer neighborhood. Its residents struggle to get the excellent schools and health care available nearby.

Natural resources also play a part in economic boundaries. Some people settle in areas rich in natural resources, like good soil for farming. These people are more likely to become wealthy. People who live in areas without many resources often stay poor.

Different groups often have different ways of life. This can sometimes cause unfair access to resources and jobs. Some of these differences include race, gender, or religion. Until 2019, in Saudi Arabia all women must had to have a man watching over them. Only he can allow that woman to travel, seek healthcare, use money, or marry. This social boundary discourages many women. They often don't seek leadership positions in business or government.

People of different races may be forced to stay in different neighborhoods. Bahrain is a Middle Eastern country. Many people from Southeast Asian countries, like Indonesia and the Philippines, have moved to Bahrain to find work. Some Bahraini political leaders forced Southeast Asians into different areas away from ethnic Bahraini people.

The nation of Sudan has many separate religious social boundaries. Northern Sudan has people who mostly follow the religion Islam. Southwestern Sudan has mostly people following Christianity. These groups fought for more than 20 years. The people of southern Sudan voted to leave Sudan as a separate nation, called South Sudan, in 2011.