A map is a symbolic representation of selected characteristics of a place, usually drawn on a flat surface. Maps present information about the world in a simple, visual way. They teach about the world by showing sizes and shapes of countries, locations of features, and distances between places. Maps can show distributions of things over Earth, such as settlement patterns. They can show exact locations of houses and streets in a city neighborhood.
Mapmakers, called cartographers, create maps for many different purposes. Vacationers use road maps to plot routes for their trips. Meteorologists—scientists who study weather—use weather maps to prepare forecasts. City planners decide where to put hospitals and parks with the help of maps that show land features and how the land is currently being used.
Some common features of maps include scale, symbols, and grids.
All maps are scale models of reality. A map’s scale indicates the relationship between the distances on the map and the actual distances on Earth. This relationship can be expressed by a graphic scale, a verbal scale, or a representative fraction.
The most common type of graphic scale looks like a ruler. Also called a bar scale, it is simply a horizontal line marked off in miles, kilometers, or some other unit measuring distance.
The verbal scale is a sentence that relates distance on the map to distance on Earth. For example, a verbal scale might say, “one centimeter represents one kilometer” or “one inch represents eight miles.”
The representative fraction does not have specific units. It is shown as a fraction or ratio—for example, 1/1,000,000 or 1:1,000,000. This means that any given unit of measure on the map is equal to one million of that unit on Earth. So, 1 centimeter on the map represents 1,000,000 centimeters on Earth, or 10 kilometers. One inch on the map represents 1,000,000 inches on Earth, or a little less than 16 miles.
The size of the area covered helps determine the scale of a map. A map that shows an area in great detail, such as a street map of a neighborhood, is called a large-scale map because objects on the map are relatively large. A map of a larger area, such as a continent or the world, is called a small-scale map because objects on the map are relatively small.
Today, maps are often computerized. Many computerized maps allow the viewer to zoom in and out, changing the scale of the map. A person may begin by looking at the map of an entire city that only shows major roads and then zoom in so that every street in a neighborhood is visible.
Cartographers use symbols to represent geographic features. For example, black dots represent cities, circled stars represent capital cities, and different sorts of lines represent boundaries, roads, highways, and rivers. Colors are often used as symbols. Green is often used for forests, tan for deserts, and blue for water. A map usually has a legend, or key, that gives the scale of the map and explains what the various symbols represent.
Some maps show relief, or changes in elevation. A common way to show relief is contour lines, also called topographic lines. These are lines that connect points that have equal elevation. If a map shows a large enough area, contour lines form circles.
A group of contour line circles inside one another indicates a change in elevation. As elevation increases, these contour line circles indicate a hill. As elevation decreases, contour line circles indicate a depression in the earth, such as a basin.
Many maps include a grid pattern, or a series of crossing lines that create squares or rectangles. The grid helps people locate places on the map. On small-scale maps, the grid is often made up of latitude and longitude lines. Latitude lines run east-west around the globe, parallel to the Equator, an imaginary line that circles the middle of the Earth. Longitude lines run north-south, from pole to pole. Latitude and longitude lines are numbered. The intersection of latitude and longitude lines, called coordinates, identify the exact location of a place.
On maps showing greater detail, the grid is often given numbers and letters. The boxes made by the grid may be called A, B, C, and so on across the top of the map, and 1, 2, 3, and so on across the left side. In the map’s index, a park’s location might be given as B4. The user finds the park by looking in the box where column B and row 4 cross.
Other Map Features: DOGSTAILS
Along with scale, symbols, and grids, other features appear regularly on maps. A good way to remember these features is DOGSTAILS: date, orientation, grid, scale, title, author, index, legend, and sources.
Title, date, author, and sources usually appear on the map though not always together. The map’s title tells what the map is about, revealing the map’s purpose and content. For example, a map might be titled “Political Map of the World” or “Battle of Gettysburg, 1863.”
“Date” refers to either the time the map was made or the date relevant to the information on the map. A map of areas threatened by a wildfire, for instance, would have a date, and perhaps even a time, to track the progress of the wildfire. A historical map of the ancient Sumerian Empire would have a date range of between 5,000 B.C. and 1,000 B.C.
Noting a map’s author is important because the cartographer’s perspective will be reflected in the content. Assessing accuracy and objectivity also requires checking sources. A map’s sources are where the author of the map got his or her information. A map of a school district may list the U.S. Census Bureau, global positioning system (GPS) technology, and the school district’s own records as its sources.
Orientation refers to the presence of a compass rose or simply an arrow indicating directions on the map. If only an arrow is used, the arrow usually points north.
A map’s index helps viewers find a specific spot on the map using the grid. A map’s legend explains what the symbols on a map mean.
Transferring information from the spherical, or ball-shaped, surface of Earth onto a flat piece of paper is called projection. A globe, a spherical model of Earth, accurately represents the shapes and locations of the continents. But if a globe were cut in half and each half were flattened out into a map, the result would be wrinkled and torn. The size, shape, and relative location of land masses would change.
Projection is a major challenge for cartographers. Every map has some sort of distortion. The larger the area covered by a map, the greater the distortion. Features such as size, shape, distance, or scale can be measured accurately on Earth, but once projected on a flat surface only some, not all, of these qualities can be accurately represented. For example, a map can retain either the correct sizes of landmasses or the correct shapes of very small areas, but not both.
Depending on the map’s purpose, cartographers must decide what elements of accuracy are most important to preserve. This determines which projection to use. For example, conformal maps show true shapes of small areas but distort size. Equal area maps distort shape and direction but show true relative sizes of all areas. There are three basic kinds of projections: planar, conical, and cylindrical. Each is useful in different situations.
In a planar projection, Earth’s surface is projected onto a plane, or flat surface. Imagine touching a globe with a piece of cardboard, mapping that point of contact, then projecting the rest of map onto the cardboard around that point. Planar projections are most accurate at their centers, where the plane “touches” the globe. They are often used for maps of one of the poles.
Imagine you wrapped a cone around Earth, putting the point of the cone over one of the poles. That is a conical projection. The cone intersects the globe along one or two lines of latitude. When the cone is unwrapped and made into a flat map, latitude lines appear curved in circles or semicircles. Lines of longitude are straight and come together at one pole. In conical projection, areas in the mid-latitudes—regions that are neither close to the Equator nor close to the poles—are represented fairly accurately. For this reason, conical projections are often used for maps of the United States, most of which lies in the mid-latitudes.
For a cylindrical projection, imagine that Earth’s surface is projected onto a tube that is wrapped around the globe. The cylinder touches Earth along one line, most often the Equator. When the cylinder is cut open and flattened into a map, the regions near the Equator are the most accurate. Regions near the poles are the most distorted.
Surveying and Remote Sensing
Cartographers rely on survey data for accurate information about the planet. Surveying is the science of determining the exact size, shape, and location of a piece of land. Surveyors gather information from regions both above sea level and beneath bodies of water.
Surveying can be done on foot. Surveyors use many instruments to measure the features, or topography, of the land. A compass, measuring device, and theodolites are often used by surveyors doing field work. A theodolite is an instrument that measures angles. A surveyor may calculate the angle of hills, valleys, and other features by using a theodolite, which is usually mounted on a tripod, or three-legged platform.
Today, many surveyors use remote sensing to collect data about an area without actually physically touching it. Sensors that detect light or radiation emitted by objects are mounted to airplanes or space satellites, collecting information about places on Earth from above. One method of remote sensing is aerial photography, taking photographs of Earth from the air. Aerial photography has eliminated much of the legwork for surveyors and has allowed precise surveying of some places that are impossible to reach on foot. Satellites, spacecraft that orbit Earth, perform remote sensing. For example, Landsat, a satellite that circles Earth 14 times a day, transmits huge volumes of data to computers on Earth. The data can be used to quickly make or correct maps.
How Maps Are Made
Before making a map, cartographers decide what area they want to display and what type of information they want to present. They consider the needs of their audience and the purpose of the map. These decisions determine what kind of projection and scale they need, and what sorts of details will be included.
The language of the map is one thing a cartographer must consider. A blind reader needs a map that has information in braille, for instance. The audience for a map can determine how widely a map is used. A map might use red and green symbols to show the location of maple and pine trees. This information might be easily displayed in a simple legend. However, such a map could not be used by people who are color-blind.
Lines of latitude and longitude are mathematically plotted on a flat surface. Features are drawn in their appropriate location.
Before the development of advanced computer and printing techniques, maps were drawn by hand. Cartographers would draw, or scribe, the map on a sheet of coated plastic with a special etching tool, scraping away the colored coating to leave clear, sharp lines. Several different sheets of plastic were layered on top of each other to add shading and place names. The plastic sheets were used to make a metal printing plate, or proof, for publishing the map.
Today, most mapping is done with the help of computers. The coordinates of every point are entered into a computer. By feeding new data into the computer or deleting old data, map changes can be made quickly and easily. Colors can be changed, new roads added, and topographic features, such as the flow of a river, altered. The new map can then be printed out easily.
Types of Maps
Cartographers make many different types of maps, which can be divided into two broad categories: general reference maps and thematic maps.
General reference maps show general geographic information about an area, including the locations of cities, boundaries, roads, mountains, rivers, and coastlines. Government agencies such as the U.S. Geological Survey (USGS) make some general reference maps. Many are topographic maps, meaning that they show changes in elevation. They show all the hills and valleys in an area. This is useful to everyone from hikers trying to choose a route to engineers trying to determine where to build highways and dams.
Thematic maps display distributions, or patterns, over Earth’s surface. They emphasize one theme, or topic. These themes can include information about people, other organisms, or the land. Examples include crop production, people’s average income, where different languages are spoken, or average annual rainfall.
Many thematic maps are now made with the help of geographic information system (GIS) technology. GIS are computer systems that capture, store, and display data related to positions on Earth’s surface. This technology combines information from maps with other data about people, the land, climate, farms, houses, businesses, and much more, allowing multiple sets of data to be displayed on a single map. Many industries and governments use GIS technology for analysis and decision making. For example, GIS data helps officials determine which streams are most in danger of being polluted. It can also help a business decide where to locate a new store.
History of Mapmaking
Through the ages, maps have taken many different forms. The earliest maps were probably sketches made on the ground that showed the surrounding area. People native to the Marshall Islands used palm fibers to show wave patterns between islands in the Pacific Ocean. They used seashells to represent islands. Inuit fishermen in the Arctic carved pieces of driftwood to show coastal features. One of the world’s oldest existing maps was found on a stone tablet in Spain. It dates back nearly 14,000 years.
The ancient Greeks are usually considered the founders of scientific cartography. Greek scholars knew the general size and shape of Earth, and they developed the grid system of latitude and longitude. Eratosthenes, who lived from about 276 to 194 B.C., calculated the size of Earth using mathematics and observations of the sun. Claudius Ptolemaeus, or Ptolemy, was an astronomer, mathematician, and geographer in the second century A.D. He brought mapmaking to a level of precision that would not be seen again until the fifteenth century. He combined all his knowledge about the world into a book called Geography.
In Europe during the Middle Ages, cartographers drew maps reflecting their religious beliefs. These maps were generally simple and sometimes fanciful. The city of Jerusalem, holy to Jews, Christians, and Muslims, was sometimes placed in the center.
Many medieval European maps with Jerusalem at the center are called T&O maps. The mass of land was represented as a round wheel encircled with a single round ocean, the “O” of the T&O. The land encircled by the ocean was divided by a “T” into the three continents known by medieval European cartographers: Asia was the large land mass above the T, Africa and Europe were the two smaller sections on either side of the T, and Jerusalem was at the center. The T-shape splitting the continents was composed of the Mediterranean Sea (between Europe and Africa), the Nile River (between Africa and Asia) and the Don River (between Europe and Asia). The Nile and the Don meet in a single line to form the top of the T.
During these Dark Ages in Europe, Arab scholars kept scientific cartography alive. They preserved the works of Ptolemy and translated them to Arabic. Arab cartographers produced the first reliable globe of the Western world.
During the Islamic Golden Age, Arab cartographers used complicated mathematical and astronomical formulas to help them determine different map projections. In 1154, the scientist and cartographer al-Idrisi made a map of the world that was better than the world maps Europeans were producing. Al-Idrisi’s map included a representation of the entire continent of Eurasia, including Scandinavia, the Arabian Peninsula, the island of Sri Lanka, and the Black and Caspian Seas.
In the fifteenth century, cartography in Europe improved. The development of printing and engraving meant maps that had previously been painted by hand could be copied more quickly. Around the same time, sailors began traveling farther on the oceans. They added newly discovered lands and more detailed coastlines to their maps. Explorers brought back descriptions of the interiors, as well as the coastlines, of continents.
Europeans explored much of the Americas during the sixteenth century, Australia in the seventeenth century, and Antarctica was finally sighted in the early nineteenth century. At this point, fairly accurate maps of the entire world were beginning to be assembled.
In the nineteenth century, cartography became more advanced with the development of a printing process called lithography. Lithography allowed cartographers to make many accurate copies of maps with less labor and expense.
Photography, color printing, and computers all improved mapmaking even more. In just a few decades, the relationship between people and maps changed drastically. For example, instead of using paper street maps, many people navigate using GPS units that communicate with satellites to determine their exact location on Earth. Digital versions of maps can represent Earth in three dimensions, defying the limitations of the flat maps of the past. Almost the entire surface of Earth has been mapped with remarkable accuracy, and this information is available instantly to anyone with an internet connection.
Eratosthenes was an astronomer, librarian, mathematician, and poet. He also invented the discipline of geography in his spare time. Using the position of the sun, Eratosthenes was able to calculate the circumference of the Earth without leaving Egypt, his home. He used the length of a stadium as his unit of distance. Because stadiums came in two different sizes in the world of ancient Greece, and we dont know which stadium Eratosthenes used, we cant know exactly what he calculated for the circumference of the Earth. If he used the larger Greek stadium, his circumference would be larger than the Earth by about 16 percent. If he used the smaller, so-called "Egyptian stadium," his calculation would still be largerbut only by 1 percent.
The Chinese were skilled cartographers. The first map was printed in China in 1155 A.D., some 300 years before maps were printed in Europe.
Using images taken from spacecraft, cartographers have created detailed maps of the surfaces of the Moon and Mars. Astrocartographers have identified Martian valleys, craters, and even dry riverbeds.
A type of cylindrical projection called a Mercator projection shows direction well. It was long used to make charts that sailors could use to find their way around the globe. Like all cylindrical projections, a Mercator projection greatly distorts the size of land near the poles. In a Mercator projection, Greenland and Africa are about the same size. In reality, Africa is 14 times the size of Greenland.
condition of being exact or correct.
picture of part of the Earth's surface, usually taken from an airplane.
(c. 1100-c. 1165) Spanish geographer and cartographer.
language that is most common in north Africa and the Middle East.
to put together.
person who makes maps of planets, moons, or other celestial bodies besides Earth.
person who studies space and the universe beyond Earth's atmosphere.
tool for measuring distance on a map.
a dip or depression in the surface of the land or ocean floor.
unable to see.
system of reading and writing for blind people using a series of raised dots.
city where a region's government is located.
person who makes maps.
physical, cultural, or psychological feature of an organism, place, or object.
people and culture focused on the teachings of Jesus and his followers.
distance around the outside of a circle.
person who plans the physical design and zoning of an urban center.
all weather conditions for a given location over a period of time.
outer boundary of a shore.
instrument used to tell direction.
symbol indicating the cardinal directions (N, S, E, W).
to transfer or make information available on computers.
representation of spatial information where angles, scale, and shape are preserved.
representation of a sphere where the surface is represented on a flattened cone, with curved lines of latitude and straight meridians.
one of the seven main land masses on Earth.
line joining points of equal elevation.
a set of numbers giving the precise location of a point, often its latitude and longitude.
geographic territory with a distinct name, flag, population, boundaries, and government.
map projection where the Earth's surface is projected onto a tube, or cylinder, shape.
structure built across a river or other waterway to control the flow of water.
(476-1000) early part of the Middle Ages in Europe, when the study of science fell out of favor.
(singular: datum) information collected during a scientific study.
area of land that receives no more than 25 centimeters (10 inches) of precipitation a year.
representation that is twisted, mistaken, or false.
the way something is spread out over an area.
pieces of wood that have traveled on currents in a body of water and drifted on shore.
to stress or place importance on.
person who plans the building of things, such as structures (construction engineer) or substances (chemical engineer).
image produced by cutting into the surface of an object.
equal area map
maps that show true relative sizes but distort shape and direction.
imaginary line around the Earth, another planet, or star running east-west, 0 degrees latitude.
(c. 276-c. 195 BCE) Greek geographer, astronomer, mathematician and poet.
landmass including the continents of Europe and Asia.
whimsical, lighthearted, or imaginary.
scientific studies done outside of a lab, classroom, or office.
to predict, especially the weather.
general reference map
map that displays general geographic facts about an area.
person who studies places and the relationships between people and their environments.
any system for capturing, storing, checking, and displaying data related to positions on the Earth's surface.
Global Positioning System (GPS)
system of satellites and receiving devices used to determine the location of something on Earth.
scale model of the Earth, or sometimes used to mean the Earth itself.
way of relating distance on a map by use of a bar scale that looks like a ruler.
horizontal and vertical lines used to locate objects in relation to one another on a map.
land that rises above its surroundings and has a rounded summit, usually less than 300 meters (1,000 feet).
representation of spatial information displaying sites of historical interest.
institution for taking care of sick or injured people.
wages, salary, or amount of money earned.
an arrangement of material in a specific type of order, usually alphabetic or numeric.
to display or show.
people and culture native to the Arctic region of Canada, Greenland, and the U.S. state of Alaska.
Islamic Golden Age
(600-1200) time period when science and art flourished in north Africa and the Middle East, where the Islamic religion is widely practiced.
body of land surrounded by water.
person who practices the Jewish religion.
large area of land.
American satellite that circles the Earth around 14 times a day.
wide-ranging activity or a big representation of an object.
distance north or south of the Equator, measured in degrees.
explanation of symbols and abbreviations used on a map, also known as a key.
labor involving travel or hard work with large tools.
printing process involving covering the printing surface with a sticky, oily substance.
distance east or west of the prime meridian, measured in degrees.
language spoken in northern China.
symbolic representation of selected characteristics of a place, usually drawn on a flat surface.
method by which shapes on a globe are transferred to a flat surface.
person who studies the theory and application of quantities, groupings, shapes, and their relationships.
having to do with the Middle Ages (500-1400) in Europe.
representation of a sphere where lines of latitude and longitude are straight and at right angles to one another.
person who studies patterns and changes in Earth's atmosphere.
(500-1500) period in European history between the Roman Empire and the Renaissance.
area between the Tropic of Cancer and the Arctic Circle in the north, and between the Tropic of Capricorn and the Antarctic Circle in the south. Also called a temperate zone.
having to do with Islam, the religion based on the words and philosophy of the prophet Mohammed.
an area within a larger city or town where people live and interact with one another.
to get or take possession of.
path of one object around a more massive object.
an object or person's position in relation to true north.
tough, flexible threads from the palm tree.
line of latitude, dividing the Earth by east-west.
area of land set aside for recreational use.
representation of volume or depth on a flat surface.
map projection where the Earth's surface is projected onto a flat surface (plane).
flat surface of two dimensions (length and width).
to form a path based on calculations.
to introduce harmful materials into a natural environment.
creating in printed form.
metal or other hard surface with raised parts that are covered in ink and pressed onto paper or another medium.
(c. 90-c. 170) Roman mathematician, astronomer and geographer.
energy, emitted as waves or particles, radiating outward from a source.
relationship between numbers or numerical values.
directly having to do with something or someone.
representation of spatial information displaying visual data for terrain.
methods of information-gathering about the Earth's surface from a distance.
to stand for a person, community, or idea.
ratio on a map that relates a distance on a map to a distance on Earth.
path or way.
person who works aboard a ship.
object that orbits around something else. Satellites can be natural, like moons, or made by people.
relationship between distances shown on a map and actual distances.
region and name for some countries in Northern Europe: Iceland, Norway, Sweden, Finland, and Denmark.
geographic area whose schools are managed by one administration.
sharp tool used to make maps using the scribing method.
method used to make maps involving a sharp tool called a scribe scraping away a color coating from a sheet of hard plastic.
base level for measuring elevations. Sea level is determined by measurements taken over a 19-year cycle.
empty shell from an organism native to the ocean, such as a snail.
spatial distribution and arrangement of human habitation.
limited in presentation or reach, unable to show details.
fixed point that, along with the North Pole, forms the axis on which the Earth spins.
exact or precise.
rounded and three-dimensional.
civilization native to Mesopotamia (modern-day Iraq) that flourished between 5000 and 1000 BCE.
a study or analysis of characteristics of an area or a population.
information gained from precisely measuring the surface of the land.
something used to represent something else.
serving as a representation of something.
representation of data on a specific topic for a specific area.
instrument used in surveying that measures angles.
to scare or be a source of danger.
T & O map
representation of the Earth used in medieval times, with a circular outline of the ocean surrounding the three known continents of Africa, Asia, and Europe.
lines on a map that connect points of equal elevation. Also called a contour line.
the shape of the surface features of an area.
human settlement larger than a village and smaller than a city.
to pass along information or communicate.
three-legged stool or platform.
count of everyone in the U.S., conducted every 10 years.
(United States Geological Survey) primary source for science about the Earth, its natural and living resources, natural hazards, and the environment.
sentence or phrase that relates distance on a map to distance on Earth.
able to be seen.
state of the atmosphere, including temperature, atmospheric pressure, wind, humidity, precipitation, and cloudiness.