A. Physical Patterns in a Changing World · Physical Patterns in a Changing World

Reading Topographic Maps and Drawing Cross-Sections

A3.3 A2.3About 50 minutes

Learning goals

I can read contour lines to find the elevation and steepness of land on a topographic map.
I can use a map's scale to measure distances.
I can draw a cross-section (profile) of a landform from a topographic map.

Words to know

topographic map
A detailed map that shows the shape and elevation of the land using contour lines, plus features like rivers, roads and buildings.

contour line
A line on a map that joins points of the same elevation.

contour interval
The difference in elevation between two side-by-side contour lines.

spot height
A dot or triangle with a number that gives the exact elevation of one point, often a hilltop.

scale
The relationship between a distance on a map and the real distance on the ground, such as 1:50 000.

cross-section
A side view of the land along a line, showing how it rises and falls.

legend
The key that explains the symbols and colours on a map.

Flattening a hill onto paper

A map is flat. Hills and valleys are not. How can a flat map show a hill?

Imagine slicing a hill like a loaf of bread, every 100 m up, and tracing around each slice from above. You'd get rings inside rings. Those rings are contour lines. Maps that use them are called topographic maps. Hikers, canoeists, engineers, farmers and First Nations, Métis and Inuit land-use planners all read them.

Forested hills and valleys with lakes stretch into the distance below a rocky lookout. — A topographic map turns a view like this into contour lines: steep hillsides get lines close together, and gentle slopes get lines far apart. AI-generated image

Remember from Grade 4

In Grade 4 you used physical maps with colours for elevation, read a legend and a scale, and looked at a cross-section of Canada. Topographic maps give you much more detail.

Reading contour lines

Each contour line joins points at the same elevation. If you walked along one, you would never go up or down.
The contour interval is the same all over one map (for example, every 10 m or every 100 m).
Lines close together = steep slope. Lines far apart = gentle slope.
Small closed rings in the middle = a hilltop or summit. A spot height may show its exact elevation.
Contour lines that bend into a V shape pointing uphill show a valley with a stream.
Contour lines never cross, because one place can't have two elevations.

Canada's official topographic maps are made by Natural Resources Canada. Many use a scale of 1:50 000, which means 1 cm on the map = 50 000 cm = 500 m on the ground.

Left: a map view of a hill with contour lines at 100, 200 and 300 m and a summit at 340 m. The lines are closer together on the east (B) side. Right: the cross-section from A to B, which is steeper on the B side. Not to scale.

Worked example

Let's draw a cross-section from A to B

Use the contour map above to draw the cross-section along the line A–B.

Lay a strip of paper along the line A–B. Mark the ends A and B.
Tick each place a contour line crosses the strip, and write its elevation (100, 200, 300, then 300, 200, 100 on the other side). Mark the summit (340 m) too.
Draw a graph frame: the horizontal axis is as long as A–B; the vertical axis shows elevation (0 to 400 m) with an even scale.
Line up the strip along the bottom of the graph. For each tick, put a dot straight above it at the correct elevation.
Join the dots with a smooth curve. Label A, B, the summit and the axes.

The cross-section rises gently from A (the 100, 200 and 300 m lines are far apart), reaches 340 m at the top, then drops steeply to B (the lines are close together).

Worked example

Let's use a scale

On a 1:50 000 map, a canoe route between two lakes measures 6 cm. How far is it on the ground?

1 cm on the map = 50 000 cm on the ground.
50 000 cm = 500 m (there are 100 cm in a metre).
6 cm × 500 m = 3 000 m.

The route is 3 000 m, or 3 km.

A scale bar for a 1:50 000 map. Each centimetre on the map stands for 500 m on the ground, so the 6 cm canoe route is 3 000 m long.

Where to find topographic maps

Free Canadian topographic maps are available from Natural Resources Canada (search "Toporama"). Many hiking and park apps show contour lines too. Try finding the hill or valley closest to your home.

Hands-on activity

Potato (or clay) contour map

You need: a potato cut in half by a grown-up (or a lump of modelling clay shaped into a hill with one steep side), a ruler, a butter knife, paper and a pencil. A grown-up should do the cutting.

Put the flat side of the potato down. This is your hill.
With the ruler, mark lines on the side every 1 cm up from the table.
Have a grown-up slice the potato flat along each mark, from bottom to top.
Trace the bottom slice on paper. Put the next slice on top in the same position and trace it inside the first. Keep going.
Label your lines 1 cm, 2 cm, 3 cm... You've made a contour map!
Where are the lines closest? That is the steepest side.
Draw a line across your map and make a cross-section using the paper-strip method.

What to look for: the rings are nested, never cross, and are closest on the steep side; the cross-section matches.

Just for fun

Why don't contour lines ever cross?

They can't agree on how high they are, so they just stay out of each other's way.

Your turn

What does a contour line join?

On a contour map, what do lines close together tell you?

What do small closed rings in the middle of a set of contours usually show?

The contour lines on a map are labelled 20, 40, 60, 80. What is the contour interval?

Why can contour lines never cross?

On a 1:50 000 map, how far on the ground is 4 cm?

In the diagram above, which side of the hill is steeper, A or B? How do you know?

More practice: warm-up

What is a map with contour lines called?

What does a scale of 1:50 000 mean?

What is a spot height?

Do contour lines far apart show a steep or gentle slope?

What part of a map explains its symbols?

More practice: on your own

A hill has contour lines at 100, 150, 200 and 250 m, and the top ring is 250 m. What is the contour interval, and what can you say about the summit's height?

On a 1:50 000 map, a trail is 7.5 cm long. How long is it in kilometres?

Contour lines make a V shape pointing uphill, with a blue line running through the V. What landform is this?

Two trails go up the same hill. On Trail 1 the contour lines are 1 mm apart; on Trail 2 they are 5 mm apart. Which trail is easier to climb? Why?

You are drawing a cross-section. A contour line labelled 300 m crosses your paper strip. Where do you put the dot on your graph?

Challenge

A cyclist wants the flattest route between two towns. Explain how she can use a topographic map to choose.

A map has a contour interval of 10 m. A path crosses 8 contour lines going uphill from a lake at 180 m. What is the elevation at the end of the path? Show your work.

Why would emergency planners use a topographic map when deciding where flood water might go?

Check your understanding

Quiz

Contour lines that are very close together show...

A contour line joins points with the same...

Lines are labelled 200, 250, 300. The contour interval is...

On a 1:50 000 map, 2 cm equals...

A side view of the land along a line on a map is a...

Small closed rings at the centre of a set of contour lines usually show...

For parents and teachers

Big idea: Expectation A3.3 asks students to extract information from and analyse topographic maps, for example by building a cross-section of a landform. A2.3 asks them to analyse and construct maps during inquiries. These are core spatial skills of geography.

How to help: Look at a free topographic map of your area (Natural Resources Canada's Toporama, or a hiking app). Find the steepest slope and the highest point. When you go for a walk or bike ride, ask, "Where would the contour lines be close together here?"

Common difficulties:

Thinking close lines mean high land: close lines mean steep, not necessarily high.
Scale conversions: remind your child 100 cm = 1 m and 1 000 m = 1 km, so 1:50 000 means 1 cm = 500 m.
Cross-sections: dots must go straight above each tick, and the vertical axis must use an even scale.

Safety: a grown-up should cut the potato.