A map is a flat drawing of a place as if you were looking down on it from above, shrunk to fit on paper or a screen. Every map uses a few tools to make sense: a scale that tells you how much smaller than real life the drawing is, a compass rose that shows which way is north, a legend (or key) that explains the symbols, and often a grid of latitude and longitude lines that gives every spot on Earth its own address. Because the Earth is round and paper is flat, every world map also uses a projection, a method of flattening the globe, and each one stretches some places out of shape. Once you know these tools, you can read almost any map, from a 2,500-year-old clay tablet to the map app on a phone.
The Babylonian Map of the World, Drawn on Clay
People were drawing maps long before paper was invented. One of the oldest surviving maps of the whole known world is a small clay tablet from ancient Mesopotamia, in what is now Iraq. It is called the Babylonian Map of the World, or Imago Mundi, which is Latin for "picture of the world".
The tablet was dug up at Sippar, about 60 km north of the ancient city of Babylon, and bought by the British Museum in London in 1882. Experts date it to no earlier than the 9th century BC, and most likely to the late 8th or 7th century BC, which makes it roughly 2,600 to 2,750 years old. The writing on it is in Akkadian, using wedge-shaped marks called cuneiform.
The map is not drawn to show real distances. It is a diagram of how the Babylonians imagined their world. The Euphrates River runs down the middle, with the city of Babylon on it. Around the edge is a ring of water the text calls the "bitter river", meaning the ocean. Beyond that are triangles pointing outward, which may stand for faraway lands or mountains. It shows that, even then, people used circles, lines and labels to stand for real things, which is exactly what maps still do.
About 150 AD, in Alexandria in Egypt, a scholar named Claudius Ptolemy wrote a book called the Geography. It listed the positions of places across the Roman world using numbers for latitude and longitude, so anyone could redraw the map from the list. His starting line for longitude ran through the Fortunate Isles, out in the Atlantic Ocean, usually linked with the Canary Islands. When Ptolemy's book was printed with maps in Bologna, Italy, in 1477, European mapmakers used it for decades.
Scale: Shrinking Britain onto an Ordnance Survey Sheet
A map is always smaller than the land it shows. The scale tells you by how much. It can be written as a ratio, such as 1:25,000, which means 1 centimetre on the map stands for 25,000 centimetres on the ground. That is 250 metres. Many maps also show a scale bar, a little ruler marked in kilometres or miles, so you can measure distances with a piece of string or the edge of a paper.
Great Britain's national mapping agency, the Ordnance Survey, shows how scale changes a map. Its work began in the 18th century, partly to map Scotland after the Jacobite rising of 1745, and by 1791 its surveyors were measuring southern Britain with a new precision instrument. Today its "Explorer" walking maps are drawn at 1:25,000, detailed enough to show single farm buildings, footpaths and field walls. Its "Landranger" maps are 1:50,000, so 1 cm stands for 500 metres. They cover twice as much ground across, but with less detail. Its road maps at 1:250,000 show whole counties at a glance, and a world map might be smaller than 1:100,000,000.
Here is the rule to remember: a large-scale map shows a small area in lots of detail, and a small-scale map shows a big area with little detail. The bigger the second number in the ratio, the more the world has been shrunk.
Finding North with a Compass Rose, from the 1375 Catalan Atlas
Most maps today are drawn with north at the top. To make sure, mapmakers add a north arrow or a compass rose, a star-shaped symbol with points for north, east, south and west. Many also show the in-between directions: north-east, south-east, south-west and north-west. A handy way to remember the order going clockwise is "Never Eat Soggy Waffles".
The compass rose grew out of sailors' charts. Mediterranean sailors in the Middle Ages used charts covered in straight lines that radiated from central points, so they could set a course from one port to another. The Catalan Atlas, usually dated 1375 and made by Cresques Abraham, a mapmaker on the Spanish island of Majorca, contains the first compass rose known on a chart like this. Its name comes from the old "wind rose", because each point was once named after a wind, such as the Greek Boreas for the north wind.
Not every old map put north at the top. Most medieval European "T and O" maps, which showed the world as a circle split into Asia, Europe and Africa, put east at the top, towards the sunrise.
Latitude, Longitude and the Line Through Greenwich
To give every place on Earth an exact address, mapmakers draw two sets of imaginary lines.
Latitude lines run east to west, like the rungs of a ladder. They measure how far north or south of the Equator you are. The Equator is 0°. It circles the middle of the Earth for about 40,075 km. The North Pole is 90° north and the South Pole is 90° south. Each degree of latitude is about 111 km apart.
Longitude lines run from pole to pole, like the segments of an orange. They measure how far east or west you are of a starting line called the Prime Meridian, which is 0°. In October 1884, delegates from many countries met at the International Meridian Conference in Washington, D.C., and recommended using the line through the Royal Observatory at Greenwich, in London. That is why visitors to Greenwich Park can stand with one foot in the Eastern Hemisphere and the other in the Western Hemisphere. Longitude goes up to 180° east and 180° west, which meet on the far side of the world in the Pacific Ocean.
Put the two together and every spot has a pair of numbers. The Royal Observatory itself sits at about 51.5° north, 0° longitude. To practise reading these numbers, try our guide to latitude and longitude for kids, and to learn how the Greenwich line also set the world's clocks, read about the history of Greenwich Mean Time.
Mercator's 1569 Map and Why Greenland Looks Huge
The only map that shows the whole Earth without stretching anything is a globe. The oldest globe that still exists is the Erdapfel, German for "earth apple", made by Martin Behaim in the city of Nuremberg between 1490 and 1492. It is 51 cm across and still sits in the Germanic National Museum in Nuremberg. It has no Americas on it at all, because Christopher Columbus did not return from his first voyage until 1493.
Globes are hard to fold into a pocket, so flat maps need a projection. Try flattening an orange peel and you will see the problem: it splits and stretches. In 1569, the Flemish mapmaker Gerardus Mercator published a giant world map, 202 by 124 cm, printed on 18 separate sheets. He made it for sailors. On his map, a line of constant compass direction is a straight line, so a navigator could draw a course with a ruler.
The price was size. Mercator's map stretches land more and more the farther it is from the Equator. Greenland looks about as big as Africa, but Africa is really about 14 times larger. Greenland covers 2,166,086 km², a little less than the Democratic Republic of the Congo. Antarctica, at the bottom, looks like an endless white strip.
Other projections fix the size problem but squash the shapes. The Gall–Peters projection, first described by James Gall in 1855 and made widely known by Arno Peters in the 1970s, shows every country at its true area, but makes Africa and South America look tall and thin. No flat map can get shape, size, distance and direction all right at once. Find out more in our guide to the Mercator projection.
Physical, Political, Topographic and Road Maps, and How to Read Their Legends
Maps are made for different jobs, and the legend tells you how each one works. The legend is the box that explains every colour, line and symbol. A blue line is usually a river, a thin black line might be a railway, and a small black square might be a building. Every mapmaker can choose different symbols, which is why you should always check the legend before you start.
- Physical maps show the land itself: mountains, rivers, lakes and deserts. They often use colours for height, with green for lowlands, then yellow and brown for higher ground, and white for the tallest peaks.
- Political maps show borders, countries, states and cities. Each country gets its own colour so you can see where one ends and the next begins. Capital cities are often marked with a star.
- Topographic maps show the exact shape of the land with contour lines. Each contour line joins points that are the same height above sea level. When the lines are bunched close together, the slope is steep, like a cliff. When they are far apart, the land is gentle or flat.
- Road maps show motorways, main roads and small lanes in different colours and widths, plus distances between towns, so drivers can plan a route.
- Thematic maps show one subject, such as rainfall, population or where different languages are spoken.
The best way to practise is to pick up a real map of your own area. Find north, check the scale, look up the symbols in the legend, and try to spot your school or a park. Then try the same thing with a world map and ask yourself which places look too big. Once you can do that, you are thinking like Mercator, Ptolemy and the Babylonian scribe who first pressed a world map into wet clay, and you are ready to explore the full system of latitude and longitude that ties all maps together.