Glossary
Earth words, explained
30 words this site uses that are worth knowing — equator, delta, hemisphere, tectonic plate — each with a short definition, a longer explanation and a real example.
Altitude
Altitude is how high a place or object is above sea level, usually measured in metres.
As altitude increases, air pressure and temperature both drop, which is why mountain tops are colder and harder to breathe on than valleys or coastlines at the same latitude. Pilots, mountain climbers and weather forecasters all rely on accurate altitude measurements.
For example: The city of La Paz in Bolivia sits at an altitude of over 3,600 metres.
Border
A border is the line where one country, state or region ends and another one begins.
Borders can follow natural features like rivers, mountain ranges or coastlines, or they can be straight lines agreed on by people, sometimes even cutting through cities or communities. Crossing a border usually means entering a place with different laws, currency and sometimes even a different language.
For example: The border between the United States and Canada includes the longest international land border in the world.
Capital City
A capital city is the city where a country's government is based and important national decisions are made.
Most countries choose one city to be their capital, usually the place where the president, prime minister or parliament works and where important laws are decided. A capital is not always the biggest or most famous city in a country, since some governments deliberately chose a smaller, more central city instead.
For example: Canberra, not the larger city of Sydney, is the capital of Australia.
Continent
A continent is one of Earth's seven huge landmasses, such as Africa, Asia or Europe.
Continents are the biggest pieces of land on Earth, each made up of many countries, mountains, rivers and cities. Geographers usually count seven continents: Africa, Antarctica, Asia, Australia, Europe, North America and South America, though some countries group a few of these together differently.
For example: Asia is the largest continent, home to countries like China, India and Russia.
Country
A country is an area of land with its own government, laws, borders and usually its own flag and currency.
Countries, also called nations or states, are the main political units the world is divided into, each recognised as having authority over its own territory and people. There are currently around 195 widely recognised countries, ranging from huge nations like Russia to tiny ones like Monaco.
For example: Japan is a country made up of thousands of islands in East Asia.
Crater
A crater is a bowl-shaped hollow, often found at the top of a volcano or formed by a falling meteorite.
Volcanic craters usually form around the opening through which lava, ash and gas erupt, and they can range from small pits to enormous basins several kilometres wide. Impact craters, formed instead by meteorites crashing into a planet or moon, can be seen clearly across the Moon's surface.
For example: Crater Lake in Oregon, USA, formed inside the collapsed crater of an ancient volcano.
Delta
A delta is new, flat land formed at a river's mouth from sediment the river drops as it slows down.
As a river approaches the sea or a lake, it loses speed and can no longer carry all the sand, silt and mud it has picked up along its course, so this sediment settles and builds up new land. Over time this new land can spread into a wide, often triangular or fan-shaped area, sometimes splitting the river into several smaller channels.
For example: The Nile Delta in Egypt spreads out in a wide triangle where the river meets the Mediterranean Sea.
Desert
A desert is a region that receives very little rain or snow each year, whether it is hot or cold.
Deserts are defined by dryness, not temperature, so they range from scorching, sandy places like the Sahara to freezing, icy places like Antarctica. Because water is scarce, only specially adapted plants and animals can survive in most desert environments.
For example: The Sahara, spanning much of North Africa, is the largest hot desert in the world.
Equator
The equator is an imaginary line around the middle of the Earth, exactly halfway between the North and South Poles.
The equator divides the Earth into a northern half and a southern half, called hemispheres, and it marks zero degrees latitude, the starting point for measuring how far north or south a place lies. Places near the equator get strong, direct sunlight all year, which is why the climate there tends to stay warm.
For example: Ecuador, a country in South America, is named after the equator, which passes almost exactly through it.
Glacier
A glacier is a huge, slow-moving mass of ice formed from compacted snow over many years.
Glaciers build up in places where more snow falls each year than melts, so layer after layer compresses into thick ice that slowly flows downhill or outward under its own weight. As they move, glaciers can carve deep valleys and carry rocks and soil for long distances.
For example: The Aletsch Glacier in Switzerland is the largest glacier in the Alps.
Hemisphere
A hemisphere is one half of the Earth, usually divided by the equator into a northern and southern half.
The word hemisphere means 'half a sphere,' and geographers split the Earth into halves in more than one way: north and south of the equator, or east and west of a chosen line of longitude. Most of the world's land and population sit in the Northern Hemisphere.
For example: Australia lies entirely within the Southern Hemisphere, south of the equator.
Island
An island is a piece of land completely surrounded by water, smaller than a continent.
Islands can form in many ways: some are the tops of underwater volcanoes, others are pieces of land left behind as sea levels rose, and some are built up from coral over thousands of years. Islands range enormously in size, from tiny sandbars to Greenland, the largest island on Earth.
For example: Iceland is a volcanic island nation in the North Atlantic Ocean.
Landlocked
A landlocked country is a country that has no coastline and is completely surrounded by other countries' land.
Landlocked countries cannot access the sea directly, which can make importing and exporting goods by ship more difficult and often more expensive, since goods must cross neighbouring countries first. There are more than 40 landlocked countries in the world, and two of them, Liechtenstein and Uzbekistan, are surrounded entirely by other landlocked countries.
For example: Switzerland is a landlocked country, bordered entirely by other European nations with no direct access to the sea.
Latitude
Latitude is a measurement of how far north or south a place is from the equator, given in degrees.
Lines of latitude, also called parallels, circle the Earth horizontally and run parallel to the equator, which sits at 0 degrees latitude. Latitude ranges from 0 degrees at the equator to 90 degrees at the North or South Pole, and it strongly affects a place's climate.
For example: New York City sits at about 40 degrees north latitude.
Longitude
Longitude is a measurement of how far east or west a place is from the Prime Meridian, given in degrees.
Lines of longitude, also called meridians, run from the North Pole to the South Pole and are used together with latitude to pinpoint any exact location on Earth. Longitude is measured from the Prime Meridian, an imaginary line through Greenwich, England, set at 0 degrees.
For example: Tokyo sits at roughly 140 degrees east longitude.
Mountain Range
A mountain range is a long chain of mountains connected together, usually formed by the same geological forces.
Mountain ranges often form where huge tectonic plates collide and push the Earth's crust upward over millions of years, or where volcanic activity builds up rock along a line. Ranges can stretch for hundreds or even thousands of kilometres, sometimes crossing several countries.
For example: The Andes, running down the western edge of South America, is the longest mountain range in the world.
Ocean
An ocean is one of Earth's five huge, connected bodies of salt water that cover most of the planet's surface.
Oceans cover about 71 percent of the Earth's surface and hold roughly 97 percent of all the planet's water. Geographers usually name five oceans: the Pacific, Atlantic, Indian, Southern and Arctic, though they are all really one connected body of water.
For example: The Pacific Ocean is the largest and deepest ocean, stretching between Asia, Australia and the Americas.
Peninsula
A peninsula is a piece of land surrounded by water on three sides but still connected to a larger landmass.
The word peninsula comes from Latin words meaning 'almost an island,' which describes it well, since water wraps around most of its edges while one side stays joined to the mainland. Peninsulas often have long, varied coastlines packed with bays, cliffs and beaches.
For example: Italy forms a long, boot-shaped peninsula stretching into the Mediterranean Sea.
Plateau
A plateau is a large area of fairly flat land that sits much higher than the land around it.
Plateaus can form when large sections of the Earth's crust are pushed upward by tectonic forces, or when layers of hardened lava build up and then get worn flat by erosion over long periods. Because they combine height with flat ground, plateaus are often used for farming or grazing animals despite their elevation.
For example: The Tibetan Plateau, sometimes called the 'Roof of the World,' is the largest and highest plateau on Earth.
Population
Population is the total number of people (or animals) living in a particular place, such as a city, country or the whole world.
Population size changes constantly as people are born, die, move into or leave an area, and countries usually count their population through a regular survey called a census. Knowing a place's population helps governments plan schools, hospitals, housing and transport.
For example: China and India are the two most populous countries, each home to more than 1.4 billion people.
Rainforest
A rainforest is a dense forest that gets very heavy rainfall all year and is home to an enormous variety of plants and animals.
Tropical rainforests grow mainly near the equator, where warm temperatures and heavy rain create ideal conditions for plants to grow quickly and densely. Although they cover only a small part of the Earth's land, rainforests are home to more than half of the world's known plant and animal species.
For example: The Amazon Rainforest in South America is the largest rainforest on Earth.
River Mouth
A river's mouth is the point where it ends, flowing into the sea, a lake or another river.
At a river mouth, the water usually slows down and spreads out, often dropping sand, mud and other sediment it has carried along its journey. Depending on how much sediment builds up, a river mouth can form a wide, fan-shaped delta or stay as a narrow, deep channel called an estuary.
For example: The mouth of the Amazon River empties into the Atlantic Ocean.
River Source
A river's source is the place where it begins, often a spring, melting glacier or mountain lake.
River sources are usually found in higher areas, such as mountains or hills, where rainwater, melting snow or underground water first collects and starts flowing downhill. A river can have one clear source or several smaller streams that join together to form its beginning.
For example: The source of the Nile is often traced to Lake Victoria in East Africa.
Sea
A sea is a body of salt water, usually smaller than an ocean and partly enclosed by land.
Seas are often connected to an ocean but are partly surrounded by coastlines, islands or narrow straits, which sets them apart from the open ocean. Some seas, like the Caspian Sea, are actually landlocked and not connected to an ocean at all, despite their name.
For example: The Mediterranean Sea lies between Europe, Africa and Asia and connects to the Atlantic Ocean.
Sea Level
Sea level is the average height of the ocean's surface, used as the zero point for measuring altitude.
Because the ocean's surface is not perfectly flat and changes with tides, scientists calculate sea level as an average measured over a long period of time at a particular location. Heights of mountains, depths of valleys and even the altitude of cities are all measured as distances above or below this reference point.
For example: Mount Everest rises about 8,849 metres above sea level, the highest point on Earth.
Summit
A summit is the highest point of a mountain or hill.
Reaching a summit is often the main goal for climbers, since it is the point from which the whole surrounding landscape can usually be seen. Some summits are sharp, rocky peaks, while others are broad, rounded or even flat, and a few are permanently covered in snow or ice.
For example: The summit of Mount Kilimanjaro in Tanzania is called Uhuru Peak.
Tectonic Plate
A tectonic plate is one of several huge, rigid pieces that make up Earth's outer shell, slowly moving over time.
The Earth's crust is broken into around a dozen major tectonic plates and several smaller ones, all floating and shifting very slowly on the hot, softer rock beneath them, usually just a few centimetres a year. Where plates meet, they can collide, pull apart or slide past each other, causing earthquakes, volcanoes and mountain ranges.
For example: The San Andreas Fault in California marks where the Pacific Plate and the North American Plate slide past each other.
Time Zone
A time zone is a region of the world that agrees to use the same standard clock time.
Because the Earth rotates and the Sun only lights up part of it at once, the world is divided into roughly 24 time zones so that clocks stay reasonably matched to daylight in each region. Travelling across time zones usually means adjusting your clock forward or backward by an hour or more.
For example: New York and London are usually five hours apart because they sit in different time zones.
Tributary
A tributary is a smaller river or stream that flows into a larger river instead of directly into the sea.
Most large rivers are fed by many tributaries joining along their course, each one collecting rainwater and runoff from its own smaller surrounding area, called a drainage basin. The point where a tributary joins the main river is called a confluence.
For example: The Missouri River is the longest tributary of the Mississippi River in the United States.
Volcano
A volcano is an opening in the Earth's crust through which hot magma, gas and ash can escape from underground.
Most volcanoes form where tectonic plates meet, either colliding or pulling apart, though some form over unusually hot spots deep inside the Earth. When a volcano erupts, it can release flowing lava, clouds of ash, or explosive blasts of rock, depending on how thick and gas-rich its magma is.
For example: Mount Vesuvius in Italy is a famous volcano that destroyed the ancient city of Pompeii in the year 79.