Seven regions: the shape of the country in one map

Killarney Provincial Park, Georgian Bay, late September. A canoe scrapes onto pink granite below a ridge of white quartzite. Jared Whitecloud is seventeen, a student from Sudbury on a school trip, and he has a question for his teacher. Why is the rock under his boots a billion years older than the rock under his aunt's house in Windsor, four hours down the highway?

So here's the question. Canada has seven landform regions, and the line between two of them is a change in rock, not a line on the ground. What are the seven, what are they made of, and what does that mean for the people on top of them?

Natural Resources Canada's Atlas of Canada draws the country as one old core, the Canadian Shield, with two rings around it: an inner ring of flat-lying lowlands and plains, and an outer ring of younger mountains. Schools split that into seven regions: the Canadian Shield, the Interior Plains, the Hudson Bay Lowlands, the Great Lakes and St. Lawrence Lowlands, the Appalachian region, the Western Cordillera, and the Arctic Lands.

How much is each? The areas come from The Canadian Encyclopedia, not a government table, so they're rounded. The Shield is roughly half of Canada. The Arctic lands are about a fifth, the Interior Plains a little less, the Western Cordillera about a sixth. The three small ones are each only 2 to 4%: the Hudson Bay Lowlands, the Great Lakes and St. Lawrence Lowlands, and Appalachia, which holds the Maritimes and Newfoundland.

The rock tells you why. Shield rock is Precambrian, billions of years old; Parks Canada dates gneiss in the Torngat Mountains to 3.9 billion. Ice scraped it bare, so it has thin soil, countless lakes, and the minerals that built Sudbury. The Plains and both Lowlands are younger sedimentary rock from shallow seas, with deep soil on top. The Cordillera and the Innuitian Mountains of the Arctic are younger still, folded and lifted.

Find it on the map. The map now shows the Atlas of Canada's physiographic regions, from Natural Resources Canada, in seven colours. Start at the legend and match each colour to its name. Now follow the Shield's colour: it wraps around Hudson Bay like a horseshoe, from Labrador to the Arctic coast. Then find the small colour holding Toronto, Montreal and Ottawa. That's the smallest region, where half of us make our homes.

Let's change one fact. Take away the last ice age. No glaciers means no scouring, so the Shield keeps its soil and loses most of its lakes. The Lowlands lose the thick clay and gravel the ice left behind, which is what grows Ontario's farms. And there is no Niagara Falls, because the falls pour off a ledge the ice uncovered. Jared's pink granite would be hidden under a forest floor.

The mistake people make is calling the Rockies the spine of Canada. The spine is the Shield. It's the oldest rock, the biggest region, roughly half the country, and the reason the middle of the map is lakes, forest and mines rather than farms. The Rockies are one belt of one region on the western edge.

Here's the rule, in one breath. One old core, two rings around it, seven regions, and the boundary between any two is a change in the rock.

This week, find which of the seven regions your home is in on the course map. Then, the next time you pass a road cut, look at the rock and ask whether it belongs to the old core or the young rings.

Next time, mountains: why Canada's highest peak isn't in the Rockies, and how to tell height from a flat map.