What this lesson teaches
I can read and choose the right maps, graphs, photographs and other visual resources.
Syllabus 9173, Fieldwork, Additional Notes on Data. Students are required to be familiar with the following types of data: Maps: contour maps, choropleth maps, isoline maps, dot maps, flow-line maps, proportional symbols maps and cartograms; Graphs: pie charts, bars, histograms, scatter graphs, radar charts, triangular graphs and line graphs; Photographs: landscape photographs, aerial photographs and satellite images; Others: tables, schematic diagrams, illustrations and cartoons.
Make a guess
On a population cartogram, a small, crowded district looks huge. Does it have a lot of land?
- No. Its size shows population, not land.
- Yes, because cartograms show land like normal maps.
- Yes, because it looks big on the map.
- It must have the most unmet need.
Show the answer
No. Its size shows population, not land.
A cartogram resizes places by a chosen variable. A district with little land but many people looks big.
A cartogram resizes places by a chosen variable, like population, so its areas no longer show land size.
A cartogram makes each place's size match a chosen quantity. A small but crowded district can look huge. This shifts attention from land area to where people, or another total, are.
Read the title and key first. In the example, districts A, B and C have equal land but populations of 100, 200 and 300. On a population cartogram, C is three times as big as A. That does not mean C has more land.
Distortion can make places hard to recognise and change their shapes and distances. Use a normal map alongside it when location or distance matters.
In a needs study, a population cartogram shows where many people need services. But it does not show unmet need. A big population may already have good access. Combine it with a rate or a measure of services.
- Cartogram
- Areas resized to match a chosen variable.
- Distortion
- Shapes and distances change.
- Limit
- Shows totals, not unmet need.
Step by step
Find the variable
What does each area represent?
Compare areas
Use the key, not real-world size.
Remember distortion
Use a normal map for distance and location.
Worked example: Right map for the task
Use the cartogram to compare population totals. Use a route map to see how far a resident travels to a clinic. The cartogram cannot show that distance.
Watch out for this
A bigger cartogram area always means higher population density.
If area shows total population, you still need real land area to work out density.
Check your understanding
On a population cartogram with the same scale, a district's area doubles between two years. What does this show?
- Its land area doubled.
- Its average journey distance doubled.
- Its population doubled.
Show the answer
Its population doubled.
Yes. Area represents population.