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.

Scale

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.

Symbols

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.

Grids

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 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.

Map Projections

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.