Map keys and symbols

Think of all the things in a town.

There are houses, roads, shops and trees. A map cannot write a name on every one. So it uses little shapes and colors instead.

Imagine drawing a map of your town and writing a label on every house, shop, tree and stream. Soon there would be more words than map! Ordnance Survey, Britain's national mapping agency, says that if it had to label everything there would be too much writing and the map would be very confusing.

So mapmakers use different shapes, colors and symbols to show the roads, buildings, rivers and other things in the landscape. A small mark can stand for something as big as a building or as long as a river.

A map symbol is a mark that stands for a real feature: a shape, a line, a pattern or a color. Symbols let a mapmaker show far more information in a small space than words ever could. Ordnance Survey explains that labeling every feature by name would leave too much writing and a very confusing map, so its maps rely on shapes, colors and symbols for roads, buildings, rivers and other features.

Symbols are also a choice about what matters. A U.S. Geological Survey (USGS) teaching lesson points out that mapmakers emphasize different characteristics of a place depending on what the map is for, so different maps of the same place highlight different features.

Most maps have a key.

The key shows each symbol. Next to it, it says what the symbol means. If you see a new symbol, look in the key.

Most maps have a key, also called a legend. It is a list that shows each symbol next to its meaning. Ordnance Survey's advice is simple: if you find a symbol you do not know, look it up in the key.

On an Ordnance Survey walking map, the key includes symbols for a railway station, an orchard, a camp site, a marsh and a viewpoint. Learning a few of them by heart makes map reading much easier.

A USGS teaching lesson puts it neatly: the legend is the key to unlocking the secrets of a map. The key, or legend, lists every symbol the mapmaker has used with its meaning. Some symbols are easy to guess, but Britannica Kids notes that others need a legend because they vary by culture, mapping custom and individual choice.

Ordnance Survey's 1:25,000-scale walking maps show how detailed a key can be: its symbols include railway stations, orchards, camp sites, marshes and viewpoints, and even a special symbol for a place of worship with a spire, a minaret or a dome. Ordnance Survey suggests asking friends and family to test you on the symbols, because once you know them, map reading becomes easy.

Some symbols are dots or little shapes.

Some are lines, like roads and rivers. Some are big patches of color, like a forest.

Map symbols come in three main kinds. Points are small marks for things in one spot, such as a well or a campground. Lines show long, thin things, such as roads, railroads, streams and borders. Areas are patches of color or pattern for things that cover ground, such as a lake or a forest.

The USGS, which makes many of the United States' maps, shows a single house as a small black square. A big building is drawn in its real shape.

The USGS guide to its topographic map symbols explains that features are shown as points, lines or areas depending on their size and extent. Point symbols mark features such as buildings, campgrounds, springs, water tanks, mines, wells and survey control points. Lines may be straight, curved, solid, dashed or dotted, and they show roads, trails, railroads, streams and boundaries.

The same feature can change category with size. On USGS maps an individual house may be a small black square, while a larger building is drawn in its actual shape. In densely built-up areas most individual buildings are left out and an area tint is shown instead, sometimes with landmark buildings such as post offices and city halls marked inside it.

Colors are clues on a map.

On some maps, blue shows water. Green shows trees and plants. Always check the key to be sure.

Colors help you read a map at a glance. On USGS topographic maps, green shows vegetation, blue shows water, and gray or red shows places crowded with buildings. Lines have colors too: brown lines show the shape of the land, blue lines show streams and rivers, red lines show important roads, and black lines show other roads, railroads and boundaries.

Other mapmakers may use different colors, so the key is always the final word.

On USGS topographic maps, the first features most readers notice are areas of color: vegetation in green, water in blue and densely built-up areas in gray or red. Line colors group similar information: brown for topographic contours; blue for lakes, streams, irrigation ditches and other water features; red for land grids and important roads; and black for other roads and trails, railroads, boundaries and other cultural features. Even place names are printed in a color that matches the type of feature.

Color rules can also change. The USGS once used purple to show revisions on its maps; it no longer does, but purple features still appear on many existing maps. And on maps from other publishers the same colors may mean something else entirely.

Not every map uses the same symbols.

One map might use a star for a city. Another might use a circle. The key on each map tells you which.

There is no single set of symbols for every map in the world. On many everyday maps, black lines are roads, lines with little tick marks are railroads, and circles or stars are cities. But each mapmaker can choose.

Colors can even be confusing. Britannica Kids explains that some maps use green and brown for forests and deserts, but others use colors to show height. Then green, meaning low land, can cover a hot, dry desert!

Symbols are conventions, and conventions differ. Britannica Kids gives a historical example: Indigenous peoples of the Americas once used cross shapes to stand for stars, while Spanish conquistadors used crosses for churches and towns. Even within one map series, the USGS notes, symbols are refined over time to match features better, read more clearly or cost less to print, so maps in the same series may show the same feature slightly differently.

Color is a common trap. Green and brown may shade real forests and deserts, but colors sometimes show elevation instead, and green used for low land can then cover a hot, dry, brown desert. The lesson for any map reader: read the key before you trust a color.

You can make up your own symbols!

Draw a map of your room. Use a little square for your bed. Then make a key to explain it.

When you draw your own map, you get to invent the symbols. Ordnance Survey shows two made-up examples in its map-reading guide, one for sport and one for a burger bar, and asks readers to guess them.

Good symbols are simple and easy to tell apart. Once you have drawn them, make a key so anyone can read your map. Then test a friend: can they find your bed, the door and the window using only your key?

Designing symbols shows why keys exist. Ordnance Survey's guide invites readers to invent their own for a sketch map, giving examples for sport and for a burger bar. A good symbol is simple, distinct from the others and, ideally, hints at what it stands for, but even a clever symbol needs a key, because a reader cannot know your intentions.

Try it with point, line and area symbols, as the USGS does: a dot or icon for a single object, a line for a path or fence, and a shaded patch for a lawn or garden. Then hand the map to someone else. Anything they cannot read without asking you is a symbol that needs a clearer design or a better key entry.