A map is a symbolic representation of selected characteristics of a place, usually drawn on a flat surface
3 - 12+
Geography, Geographic Information Systems (GIS)
Maps present information about the world in a simple, visual way. They show the shapes of countries, locations of bodies of water or mountains, and distances between places. Maps can also show the layout of a single city's streets.
Mapmakers are known as cartographers. They create maps for many different purposes. Tourists use road maps to plot routes for their trips. City planners use maps to help them decide where to put hospitals and parks.
Maps often have the same basic elements. These elements include the map's scale, symbols, and grids.
A map's scale shows the relationship between distances on the map and the real distances on Earth. For example, a map might say, "one inch represents eight miles." Scales might also be shown as fractions or ratios. For example, the scale might be 1/1,000,000 or 1:1,000,000. This means that any given unit of distance on the map is equal to one million of that unit on Earth. So, one inch on the map represents 1,000,000 inches on Earth, or a little less than 16 miles. Most maps use a visual scale that looks like a ruler. It is simply a horizontal line marked off in miles or kilometers.
If a map shows an area in detail, it is called a large-scale map because the objects shown are relatively large. For example, a street map of a neighborhood is a large-scale map. If a map shows a larger area, like a continent, it is called a small-scale map. In this case, objects on the map are small compared to the real-life continent.
A symbol is something that stands for something else. Cartographers use symbols to represent geographic features. For example, black dots represent cities and circled stars represent capital cities. Different sorts of lines represent boundaries, roads, highways, and rivers. Colors are often used as symbols, too. Green is usually used for forests, tan for deserts, and blue for water.
Some maps show elevation, or height. This is especially useful when the maps have mountains, hills, or craters. Elevation is shown by symbols known as contour lines. Each line shows a change in elevation, as if the object was sticking out or sinking into the flat map.
Maps usually have a legend. A legend is a key that shows the scale and also explains what the symbols mean.
Many maps include a grid. A grid is a series of crossing lines that create squares or rectangles. A map's grid helps people locate specific places.
On small-scale maps, the grid is often made up of latitude and longitude lines. Latitude lines run east-west around the globe. They run parallel to the Equator, an imaginary line that circles the middle of Earth. Longitude lines run north-south, connecting the North and South Poles.
Latitude and longitude lines are numbered. The points where they intersect, or cross each other, are called coordinates. These coordinates indicate the exact location of a place.
On large-scale maps, the grid is often marked by numbers and letters. The boxes made by the grid may be called A, B, C, and so on across the top of the map. Across the left side, they may be called 1, 2, 3, and so on.
These numbers and letters help find things on the map. For example, suppose you wanted to find a particular park. First, you would look at the map's index. An index is a list of all the places and things shown on a map. It appears on the bottom or back of a map. Say that the index gave the park's location as B4. You would find the park by looking in the box that's in column B and row 4.
Other Map Features
Maps usually have a title and date. The map's title says what the map is about. For example, a map might be titled "Map of Africa" or "Battle of Gettysburg, 1863."
The date refers to either the time the map was made or the time period covered by the map. For example, a map covering World War II might be dated 1939 to 1945.
It is also helpful to know the orientation of a map. Orientation is the relationship between the directions on a map and real-life compass directions. A map's orientation can be given by a compass rose or simply an arrow. If only an arrow is used, the arrow usually points north. Most modern maps show north on the top.
Earth is almost spherical, or ball-shaped. Most maps are flat. Drawing the round surface of Earth onto a flat map is called projection.
Projection is a major challenge for cartographers. To understand why, think of a globe. If a globe is cut in half and each half is flattened out into a map, the result is distorted. That means size and distances are stretched or compressed.
Every map has some distortion. The larger the area covered by a map, the greater the distortion. Size, shape, distance, and scale cannot all stay accurate after they are projected on a flat surface.
Depending on the map's purpose, cartographers must decide what elements should stay accurate. Different types of projection keep different elements. Conformal maps show true shapes of small areas but distort relative size. One area that is actually smaller than another may appear to be larger. Equal-area maps distort shape, but show true relative sizes.
There are three basic kinds of projections: planar, conical, and cylindrical. Each is useful in different situations.
In a planar projection, the surface of Earth is projected onto a flat surface. Imagine touching a globe with a piece of cardboard. Now, imagine projecting the rest of the globe onto the cardboard, while holding it at that fixed point. The result is a planar projection. This kind of projection is most accurate at the center point. Planar projections are often used for maps of one of the poles.
Now, imagine wrapping a cone around Earth, with the point of the cone over one of the poles. That is a conical projection. When the cone is unwrapped and made into a flat map, latitude lines look like circles or semicircles. Lines of longitude are straight and come together at one pole. In conical projections, the most accurate areas are between the Equator and the poles.
Finally, we have cylindrical projections. 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.
How Maps Are Made
Surveying is the science of measuring the size, shape, and location of a piece of land. Today, many surveyors use remote sensing to make measurements. Sensors are mounted to airplanes or space satellites. They collect geographic information from above.
Before computers and printing, cartographers drew maps by hand. Today, most mapping is done with computers. The coordinates of every point are entered into a computer. By adding new information into the computer or deleting old information, map changes can be made quickly and easily.
Cartographers make different types of maps, which can be divided into two main categories: general reference maps and thematic maps.
General reference maps show general geographic information about an area. They include the locations of cities, boundaries, roads, mountains, rivers, and coastlines. Many are topographic maps, meaning that they show changes in elevation. They show all the hills and valleys in an area.
Thematic maps show information about people, other organisms, or concepts. They might show where people speak a certain language, or how much they earn.
History of Mapmaking
Through the ages, maps have taken many forms. The earliest maps were probably sketches made on the ground. 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 were the first to create scientific cartography. Greek scholars knew the general size and shape of Earth. They also developed the grid system. Ancient Greek mapmaking reached a level of accuracy that wasn't seen again until the 1400s.
In Europe during the Middle Ages, maps became much less accurate. Cartographers drew maps based on their religious beliefs. These maps were generally simple and often quite wrong. During this period, Arab scholars kept scientific cartography alive. Arab cartographers produced the first accurate globe of the Western world.
In the 1400s, cartography in Europe finally began to improve. In part, this was because European sailors had begun traveling farther on the oceans. They added newly discovered lands and more detailed coastlines to their maps. By the 1800s, fairly accurate maps of the entire world were being made.
In recent times, computers have expanded what maps can do. Many computer maps allow viewers to zoom in and out, changing the scale of the map. Almost the entire surface of Earth has been mapped with very high accuracy. 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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November 30, 2023
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