Amapis asymbolicrepresentation of selectedcharacteristics 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 showdistributions of things over Earth, such assettlement patterns. They can show exact locations of houses and streets in a cityneighborhood.
Mapmakers, calledcartographers, create maps for many different purposes. Vacationers use road maps toplotroutes for their trips.Meteorologists—scientists who study weather—use weather maps to prepareforecasts.City planners decide where to puthospitals andparks with the help of maps that show land features and how the land is currently being used.
Some common features of maps includescale,symbols, andgrids.
All maps are scale models of reality. A map’s scaleindicates 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 ofgraphic scalelooks like a ruler. Also called abar scale, it is simply a horizontal line marked off in miles, kilometers, or some other unit measuring distance.
Theverbal scaleis 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.”
Therepresentative fractiondoes not have specific units. It is shown as a fraction orratio—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 alarge-scalemap because objects on the map are relatively large. A map of a larger area, such as acontinentor the world, is called asmall-scalemap because objects on the map are relatively small.
Today, maps are oftencomputerized. 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 representcapitalcities, and different sorts of lines represent boundaries, roads, highways, and rivers. Colors are often used as symbols. Green is often used for forests, tan fordeserts, and blue for water. A map usually has alegend, 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 iscontour lines, also calledtopographic 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 ahill. As elevation decreases, contour line circles indicate a depression in the earth, such as abasin.
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 oflatitudeandlongitudelines. Latitude lines run east-west around theglobe, parallel to theEquator, 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, calledcoordinates, 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 daterelevantto 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. Ahistorical mapof the ancientSumerian Empirewould 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’sperspectivewill be reflected in the content. Assessingaccuracyand 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 theU.S. CensusBureau,global positioning system (GPS)technology, and the school district’s own records as its sources.
Orientation refers to the presence of acompass roseor 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 aspecificspot on the map using the grid. A map’s legend explains what the symbols on a map mean.
Transferring information from thespherical, 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 ofdistortion. 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 aplanar 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 aconical 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 themid-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 acylindrical 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 onsurvey datafor 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 abovesea leveland beneath bodies of water.
Surveying can be done on foot. Surveyors use many instruments to measure the features, ortopography, of the land. Acompass, measuring device, and theodolites are often used by surveyors doingfield work. Atheodoliteis 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 atripod, or three-legged platform.
Today, many surveyors useremote sensingto collectdataabout an area without actually physically touching it. Sensors that detect light orradiationemitted by objects are mounted to airplanes or spacesatellites, collecting information about places on Earth from above. One method of remote sensing isaerial photography, taking photographs of Earth from the air. Aerial photography haseliminated much of thelegworkfor 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. Ablindreader 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, orscribe, 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 metalprinting 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 andthematic maps.
General reference maps show general geographic information about an area, including the locations of cities, boundaries, roads, mountains, rivers, andcoastlines. 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 toengineers trying to determine where to build highways anddams.
Thematic maps display distributions, or patterns, over Earth’s surface. Theyemphasizeone theme, or topic. These themes can include information about people, other organisms, or the land. Examples includecropproduction, people’s average income, where different languages are spoken, or average annual rainfall.
Many thematic maps are now made with the help ofgeographic 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 officialsdeterminewhich streams are most in danger of beingpolluted. 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 usedpalm fibers to show wave patterns between islands in the Pacific Ocean. They usedseashells to representislands.Inuitfishermen in the Arctic carved pieces ofdriftwoodto 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. Greekscholars 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, orPtolemy, was anastronomer, mathematician, andgeographerin 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 calledGeography.
In Europe during theMiddle Ages, cartographers drew maps reflecting their religious beliefs. These maps were generally simple and sometimesfanciful. The city of Jerusalem, holy toJews,Christians, andMuslims, 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 bymedievalEuropean 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 theseDark Agesin 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 theIslamic Golden Age, Arab cartographers used complicated mathematical and astronomical formulas to help them determine different map projections. In 1154, the scientist and cartographeral-Idrisimade 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 ofEurasia, includingScandinavia, 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 andengravingmeant 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 calledlithography. 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.
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.
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 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 don't know which stadium Eratosthenes used, we can't know exactly what he calculated for the circumference of Earth. If he used the larger Greek stadium, his circumference would be larger than Earth by about 16 percent. If he used the smaller, so-called "Egyptian stadium," his calculation would still be largerbut only by 1 percent.
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.
The Chinese were skilled cartographers. The first map was printed in China in 1155 C.E., some 300 years before maps were printed in Europe.
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