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Marks that stand for things, the list that explains them, and why a symbol's size proves nothing.
Paper packet. Every task here also exists on screen, where it is checked automatically; answers written on paper are not assessed by Nydus. When you are back at a device, enter your answers there.
You will read a map's key, use it to find things on the map, and say why the size of a symbol does not tell you the size of the thing.
You already know that a plan is drawn from straight above, so each thing on it is a patch of ground. This lesson is about what fills that patch in: a mark that stands for the thing, and a list saying which mark is which. You will also use multiplication, because sometimes one mark stands for many things.
| Term | What it means |
|---|---|
| Symbol | A mark on a map that stands for a real thing. |
| Key | The list that says what each symbol stands for on this map. |
| Legend | Another name for a map's key. |
| Stand for | To take a thing's place: the blue patch stands for water. |
A map is too small to draw a pond as a pond and a bench as a bench. So a map uses symbols: marks that stand for things. A blue patch stands for water. A green circle stands for a tree. A gray strip stands for a path.
Nothing makes those the right marks. The mapmaker chose them, and somebody else drawing the same park could choose differently. That is why every map carries a key: a little list, usually in a corner, saying what each mark on this map stands for.
Read the key first. A map without its key is a pattern.
Another way: story
Think of the key as the map introducing itself: on me, blue means water. A different map may say on me, blue means a bus route, and it is not wrong; it is a different map saying so.
Another way: example
Two things on the park plan are gray: the path and the parking lot. The key tells them apart by shape, a strip and a bordered rectangle, which is why a key line gives you both the color and the shape.
Here is the key to the park plan this course uses.
| Mark | Stands for |
|---|---|
| a blue patch | water |
| a small green circle | a tree |
| a yellow square | play equipment |
| a gray strip | a path |
| a gray rectangle with a dark border | a parking lot |
| a small brown block | a gate |
Each line has two parts: the mark as it is drawn, and what it stands for. Read the whole line. A mark's color and its shape are both part of it.
Some colors are used the same way on so many maps that they feel like rules. Water is almost always blue. Woods and parks are often green. Roads are often red, black or gray.
These are habits, not laws. A subway map may use blue for one train line and green for another, and neither has anything to do with water or grass. The habit helps you guess, but only the key tells you for sure.
Symbols come in three main kinds. A point symbol, such as a dot, a star or a small picture, marks one spot: a mailbox, a school, a campsite. A line symbol marks something long and thin: a road, a river, a trail. An area symbol fills a patch: a lake, a forest, a parking lot.
When two things share a color, the shape often settles it. A gray line is a path; a gray patch is a parking lot.
Many maps use small pictures as symbols. A tent means a campsite, an airplane means an airport, a book means a library. National park maps use pictures like these so that people who speak different languages can read them.
A picture symbol still needs the key. A cup might mean a café on one map and a water fountain on another. The key is where the mapmaker says which.
Sometimes a map has too many things to draw one mark each. Then the key can say that one symbol stands for a group: one tree symbol for ten trees, or one person symbol for a hundred people.
To count, multiply. If one tree symbol stands for ten trees and a wood has six symbols, the wood has six times ten, which is sixty trees. It is the same idea as a picture graph in math class, where one picture stands for several things.
A symbol is as big as it needs to be to see. The mapmaker chose it, and the choice says nothing about the size of the thing on the ground: one small circle stands for a tree whether the tree is a sapling or the oldest oak in the county.
A mailbox might get a big red dot so you can spot it, and a big lake might get a patch smaller than it should because the page is small. If you want to know how big something really is, look at the scale bar, not at the symbol.
Checking an answer. Read the key line again and check that your mark matches both its color and its shape. If another mark matches too, look for what makes them different.
Reading the key first is allowed, and needed, because the mapmaker chose the marks: only the mapmaker's own list can tell you what they mean.
Multiplying is allowed when every symbol stands for the same number, because then each symbol is an equal group, and equal groups are what multiplication counts. Ignoring a symbol's size is allowed because the key never promised that size means anything.
The most common slip is guessing from color without reading the key. It works until two things share a color. Another is reading only half a key line, the color and not the shape.
A third is taking a big symbol to mean a big thing. A fourth, on maps where one symbol stands for many, is counting the symbols and forgetting to multiply.
Every visitor to a U.S. national park can pick up a free map at the entrance. The maps are made by the National Park Service, and they all share one set of symbols, so a family who learns them at the Grand Canyon can read the map at Yellowstone or the Great Smoky Mountains.
The key uses small pictures inside squares. A tent means a campground. A picnic table means a picnic area. A figure walking means a trailhead, where a hiking path begins. A wheelchair means a place that people in wheelchairs can reach. Lines are used for roads and trails, and patches of color for lakes and forests.
Pictures like these work even for visitors who do not read English well, which matters in parks that welcome people from all over the world. But even picture symbols are choices. Before a hike, a careful hiker still reads the key, because a dashed line might mean a paved path on one map and a rough trail on another, and the difference could decide whether the walk takes an hour or a day.
The New York City subway map gives each group of train lines its own color. The 4, 5 and 6 trains are green; the A, C and E trains are blue; the 1, 2 and 3 trains are red. Riders learn to say "take the green line" without thinking.
Here blue does not mean water and green does not mean grass. The colors are symbols with meanings chosen by the mapmakers, and the key on every map in every station says which is which. Rivers and bays are shown too, in pale blue, so the key has to keep a river from being mistaken for a train line.
The map also uses shapes. A white circle marks a station where all trains stop, and a black dot marks a station where only local trains stop. A rider who reads the whole key line, color and shape, knows which train to take and where to get off. A rider who guesses from color alone may end up on the right line going the wrong way.
The first trap is guessing instead of reading. Blue usually means water, so guessing works, until the map has two gray things on it, and then it fails completely. Read the key line: it gives a color and a shape.
The second trap is size. A symbol is as big as it needs to be to see. The mapmaker chose it, and the choice says nothing about the size of the thing on the ground: one small circle stands for a tree whether the tree is a sapling or the oldest oak in the county.
So a gate drawn as a fat brown block is not a fat gate. It is a narrow thing given enough ink to see. If you want to know how big something really is, the scale bar tells you; the symbol never does.
The key says a blue patch is water. Find that line.
$\text{blue patch: water}$
That is the line you need.
Look for blue on the plan.
$\text{one blue shape}$
The oval in the corner.
Check for other blue marks.
$\text{none}$
So nothing else is water.
Name what you found.
$\text{the pond}$
The key settles it, not a guess.
The key says a gray strip is a path and a gray bordered rectangle is a parking lot.
$\text{same color, different shape}$
Two key lines.
Try color alone.
$\text{both are gray}$
Color cannot decide it.
Read the shapes.
$\text{a strip; a bordered rectangle}$
Long and thin, or wide.
Name the long thin mark.
$\text{the path}$
It matches the whole line.
Name the wide mark.
$\text{the parking lot}$
A key line is the whole line.
A key says one tree symbol stands for $10$ trees. Read the key line.
$1 \text{ symbol} = 10 \text{ trees}$
Each symbol is a group.
The wood has $6$ symbols. Count its trees.
$6 \times 10 = 60$
Six equal groups.
The orchard has $4$ symbols. Count its trees.
$4 \times 10 = 40$
The same key line.
Add the two places.
$60 + 40 = 100$
All the trees.
Check by counting symbols first.
$6 + 4 = 10 \text{ symbols}; 10 \times 10 = 100$
The same answer.
Say what would go wrong without the key.
$\text{you would count } 10 \text{ trees}$
The key says what a symbol is worth.
Find the key line for brown.
$\text{brown block: gate}$
Read the key first.
Find the brown marks on the plan.
$\text{one, at the bottom edge}$
Where the path meets the fence.
Name the brown mark.
Here are three marks from the key of a park plan. What does each one stand for?
| a gate | a parking lot | a path | |
|---|---|---|---|
| a brown block | |||
| a gray rectangle with a border | |||
| a gray strip |
Complete the worked solution: the key of a state park map says one tree symbol stands for $5$ trees. The map shows $7$ tree symbols in the wood and $3$ in the orchard. How many trees grow in each, and in both together?
Count the trees in the wood.
$\text{symbols} \times \text{trees per symbol} =$ w
The key says how many each stands for.
Count the trees in the orchard.
$\text{symbols} \times \text{trees per symbol} =$ o
The same key line.
Add the two places.
$\text{wood} + \text{orchard} =$ t
All the trees.
Say what the key decided.
$\text{what one symbol is worth}$
The map alone cannot say.
Now the other way around. The mapmaker is drawing the park. Which mark should each of these get?
| a gray strip | a brown block | a yellow square | |
|---|---|---|---|
| the path to the gate | |||
| the gate on to the road | |||
| a set of swings |
The key to this park plan says: a blue patch is water, a green circle is a tree, a yellow square is play equipment, a gray strip is a path. Click the water.
This task has no paper form; do it on a device.
The park plan was printed without its key. Put each mark's meaning back.
| What it stands for | |
|---|---|
| a blue patch | |
| a small green circle | |
| a gray rectangle with a dark border |
Two things on this plan are gray. The key says a gray **strip** is a path and a gray **rectangle with a dark border** is a parking lot. Click the path.
This task has no paper form; do it on a device.
A different map, with a key you have never seen. The map of Kestrel Island says: a gray triangle is a hill, small yellow humps are sand dunes, a red block with a yellow light on top is a lighthouse, and small gray blobs are rocks a boat must avoid. Match each mark to what it stands for.
| a hill | sand dunes | a lighthouse | |
|---|---|---|---|
| a gray triangle | |||
| small yellow humps in a row | |||
| a red block with a yellow light on top |
Lesson test: one question per skill, one attempt each, no hints. Your answers are checked when you submit.
A new community garden map uses one leaf symbol for 5 planted trees. The orchard patch has 6 leaf symbols. Complete the table for the current orchard and a revised plan with two additional leaf symbols. Count represented trees, not the size of the marks.
| Represented trees | |
|---|---|
| Current orchard | |
| Revised orchard: two more symbols |
You can read a key and use it. Tell somebody why two gray marks on one map can mean two different things, and where you would look to settle it.
20. Your turn: the key says a brown block is a gate. What is the brown mark at the bottom edge?, step 3
$\text{the gate}$
Color and shape both match.