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Every map is somebody's answer to somebody's question, and choosing what to leave off is most of the job.
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 work out what a map was made for, say what it leaves out and why, and explain why a symbol's size is a decision rather than a measurement.
You can already read a key and find what a mark stands for. So you know that everything on a map was put there by somebody. This lesson asks the other half of that question: what did they decide not to put on?
| Term | What it means |
|---|---|
| Purpose | The job a map was made to do. |
| Leave out | To decide not to draw something, on purpose. |
| Choice | A decision the mapmaker made that the ground did not make for them. |
| Title | The words at the top of a map that say what it shows. |
Nobody can draw everything. A map showing every trash can, every crack in the sidewalk and every blade of grass would have to be as big as the place itself, and then you could not carry it.
So a mapmaker chooses. They ask what the map is for, put in what helps with that, and leave out everything else. A bus map leaves out the streets no bus uses. A hiking map leaves out the bus routes and puts in how steep the hills are.
None of those maps is lying. Each is an answer to a different question, and the first thing to ask of a map you have not seen before is: what was this made for?
Another way: story
If a friend asks you the way to the store, you do not describe every house you pass. You say left at the mailbox, then it is on the right. You left out almost everything, and that is why the directions worked.
Another way: example
Three maps of one town: a street plan names the streets, a bus map draws the routes, a weather map shows tomorrow's rain. All three are of the same town, and no two of them show the same things.
Read this little plan as if you were looking straight down: the roof hides the walls, so a building appears as its footprint. A key can use a square for a shed and a tree-shaped mark for a tree. Read the key before naming either. A plan made to find paths may omit bird sightings or heights. That omission means the map cannot answer those questions; it does not mean there are no birds or tall objects. To give a position on a numbered grid, read the column from the left and then the row from the bottom. The square in column 2 and row 3 is (2, 3). These numbers name a patch of the plan, not the height or size of its shed.
Here is what four maps of the same town might keep and leave out.
| Map | Keeps | Leaves out |
|---|---|---|
| street plan | every street and its name | bus routes, hills |
| bus map | bus routes and stops | most streets |
| hiking map | trails and how steep the hills are | bus routes, most buildings |
| weather map | tomorrow's rain and temperatures | streets, buildings, buses |
No map on the list is better than the others. Each one is best at its own job.
Leaving things out is not laziness. Every extra line on a map makes the lines that matter harder to see. A bus map covered in every street would bury the bus routes in a tangle.
So mapmakers clear away what the reader does not need, the way you clear a desk before doing homework. What is left stands out, and the reader finds the answer quickly.
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.
On a map of a whole state, a town might be a dot the size of a pencil point, though the real town is miles across, and a highway might be a red line wider than a city block would be at that size. Those sizes are choices made so the reader can see things, not measurements.
Mapmakers also smooth things out. A real river bends in thousands of tiny wiggles; a map of a whole state draws it as a gentle curve. A real coastline has every rock and cove; a map of the country shows it as a smooth line.
The smaller the map, the more has to be smoothed or left off, because there is less room. A map of your street can show every house; a map of your state cannot even show every street.
Most of a place never makes it onto any one map. Picture a park with eight benches, five trash cans and four flowerbeds, and a plan for drivers that shows only six things: the gate, the parking lot, the path, the pond, the play area and the trees.
The plan leaves off eight plus five plus four, which is seventeen things, and shows six. The park has seventeen plus six, twenty-three things, and the plan leaves off most of them. It is still a good plan, because it keeps what drivers need.
Because every map leaves things out, a good map says what it is for. Usually that is the title: Bus Routes of Springfield, Hiking Trails of Pine Lake.
The title warns you what not to expect. If you look for a street on a map titled Bus Routes and cannot find it, the street is not gone; the map was never meant to show it.
Checking an answer. Ask whether the thing you are looking for would help with the map's job. If it would not, do not expect it on the map.
Reading the title first is allowed because the title is the mapmaker telling you the job. Asking who the map is for is allowed because mapmakers choose what to keep with their readers in mind.
Judging a map by its job is fair, because no map can do every job. A map should be blamed for leaving out what its own job needs, not for leaving out what another map's job needs.
The most common slip is thinking a map shows everything that is there, and so deciding that something missing from the map is missing from the ground. Another is calling a map wrong because it was made for a different job.
A third is reading a symbol's size as the thing's real size. A fourth is picking the map that looks nicest instead of the one made for your question.
The National Oceanic and Atmospheric Administration, called NOAA, makes maps for boats along every coast of the United States. These maps are called nautical charts, and they look very different from a road map of the same place.
A chart of a harbor shows how deep the water is, with small numbers scattered across the blue. It shows rocks just under the surface, sunken wrecks, buoys that mark safe channels, and lighthouses with notes on how their lights flash. On land it shows almost nothing: a few tall towers and steeples that sailors can see from the water, and little else. Streets, schools and stores are left off.
A driver would find the chart useless, and a sailor would find a road map dangerous, because it shows none of the rocks. Both maps are honest. Each keeps exactly what its readers need to stay safe and leaves out the rest. The title on every chart says which stretch of coast it covers and that it is made for navigation, so nobody mistakes it for a road map.
Riders of the subway in Washington, D.C., use a map that shows six colored lines and the stations along them. It leaves out nearly every street in the city. It even bends the lines into neat straight runs and smooth corners, though the real tunnels curve and wander under the ground.
That sounds like a lot of mistakes, but each one is a choice. A rider needs to know which line to take, which stations come next and where to change trains. Streets would crowd the map, and true curves would make the stations hard to read. So the mapmakers kept the order of the stations and the places where lines meet, and let everything else go.
The map is not good for measuring distance: two stations that look close may be far apart. It was never meant for that. For walking between stations, riders use a street map, which leaves out the train lines' neat shapes but keeps every street.
The first belief to give up is that a map shows everything that is there. No map does. When two maps of one place disagree, it is usually because they were made for two different jobs, and the useful question is which job, not which map is lying.
The second is the one this course keeps returning to. 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 fat symbol is not a fat thing.
The third is quieter: a map that leaves something out is not admitting it. That is why a good map carries a title saying what it is, and why the last lesson of this course goes back and asks each of our maps to say who made it and when.
A bus map shows the routes but few streets. Ask what it is for.
$\text{which bus goes where}$
That is the job.
Picture every street drawn in.
$\text{lines across the routes}$
They would hide the answer.
Judge leaving them out.
$\text{a better bus map}$
Clearer for riders.
Say what the map must still do.
$\text{say it is a bus map}$
So nobody looks for streets on it.
A gate is narrower than the path it opens onto. Picture it at true size.
$\text{thinner than the ink}$
Nobody could find it.
Say what the mapmaker did.
$\text{drew it bigger}$
So readers can find it.
Name the kind of decision.
$\text{a choice about ink}$
Not a fact about the gate.
Say where the real size is.
$\text{the scale bar}$
Measure with it instead.
State the rule.
$\text{symbol size proves nothing}$
A fat symbol is not a fat thing.
A drivers' plan of a park leaves off $8$ benches, $5$ trash cans and $4$ flowerbeds. Add them.
$8 + 5 + 4 = 17$
Things left off.
It shows $6$ things. Find everything in the park.
$17 + 6 = 23$
Left off plus shown.
Compare left off with shown.
$17 > 6$
Most is left off.
Ask what the plan was for.
$\text{arriving by car}$
Its job.
Check what it kept.
$\text{gate, parking lot, path}$
What drivers need.
Judge the plan.
$\text{good for its job}$
Leaving out is not a fault.
Ask what the map is for.
$\text{finding the way on foot}$
Its readers are hikers.
Ask what hikers need.
$\text{the trail}$
To follow it.
Judge the farm's name.
On the park plan the gate is drawn as a brown block about as wide as a tree's circle. On the ground the gate is narrower than the path beside it. Why is the gate's block drawn so big?
Complete the worked solution: a park plan made for families arriving by car leaves off the park's $8$ benches, $5$ trash cans and $4$ flowerbeds. It shows $6$ things. How many things does it leave off, and how many things are in the park altogether?
Add up what is left off.
$\text{benches} + \text{trash cans} + \text{flowerbeds} =$ l
None helps with arriving.
Add what is shown.
$\text{left off} + \text{shown} =$ a
Everything in the park.
Compare the two counts.
$\text{more left off than shown}$
Most of a place is left off.
Judge the plan.
$\text{still a good plan for its job}$
It keeps what drivers need.
A town's bus map does not show most of the streets in the town. Is that a fault in the map?
Match each question to the map that was made to answer it.
| a bus map | a walking map with contour lines | a street plan of the town | |
|---|---|---|---|
| which bus goes to the hospital | |||
| how steep the hill above the village is | |||
| which street the library is on |
This plan was made for a family arriving by car. It does not show the benches, the trash cans or the flowerbeds; none of those helps with arriving. Click the part of the plan that was put there for exactly this family.
This task has no paper form; do it on a device.
Three people want to know three different things. Say which kind of map each of them needs.
| The map to use | |
|---|---|
| Which street is the library on? | |
| Which bus goes to the hospital? | |
| Will it rain on the coast tomorrow? |
This map of Kestrel Island was drawn for people in boats. It shows the lighthouse, the bay where you can land, and the rocks, and it shows no footpaths at all, because a boat cannot use one. Click the mark that is on it to warn a boat to keep away.
This task has no paper form; do it on a device.
An invented garden plan seen straight from above has this key: square = shed footprint, tree symbol = tree, blue patch = pond. It shows where things stand, but omits their heights and the birds seen yesterday. A visitor needs the shed, not the tree or pond. Place the shed label in its grid square. Read columns from the left and rows from the bottom.
This task has no paper form; do it on a device.
Lesson test: one question per skill, one attempt each, no hints. Your answers are checked when you submit.
An invented garden plan seen straight from above has this key: square = shed footprint, tree symbol = tree, blue patch = pond. It shows where things stand, but omits their heights and the birds seen yesterday. A visitor needs the shed, not the tree or pond. Place the shed label in its grid square. Read columns from the left and rows from the bottom.
This task has no paper form; do it on a device.
You can say what a map was made for. Tell somebody why a bus map with no street names on it is a good map rather than a careless one.
21. Your turn: a hiking map shows a trail through a field but does not name the farm. Why not?, step 3
$\text{no help finding the way}$
So it was left off.