To interpret an urban-growth pattern, describe the change in numbers, compare the periods and then describe where on the map the change happens. It appears with maps, satellite-style images and tables in population and settlement evidence.
How do you interpret step by step?
- Name the measure and unit, for example built-up area in km².
- Find the change for each period, in absolute terms.
- Work out the percentage change if the question asks you to compare.
- Identify the fastest and slowest periods.
- Describe the shape on the map: direction, routes followed, edges.
- Add a limit: the data may not show why growth happened.
Worked example
Invented data for City E, built-up area.
| Year | Built-up area (km²) |
|---|---|
| 1990 | 40 |
| 2000 | 55 |
| 2010 | 90 |
| 2020 | 110 |
Absolute change: 1990 to 2000: 15 km². 2000 to 2010: 35 km². 2010 to 2020: 20 km².
Percentage change 2000 to 2010: 35 ÷ 55 = 0.6364, so 63.6%.
Per year, 2000 to 2010: 35 ÷ 10 = 3.5 km² per year.
Over the whole period: 110 − 40 = 70 km², and 70 ÷ 40 = 1.75, so 175% growth.
Description: “City E’s built-up area grew fastest between 2000 and 2010, by 35 km² or 63.6%. Growth then slowed to 20 km² in 2010 to 2020.” Suppose the map shows new buildings along the northern road. Then add: “New housing is stretched along the northern road, a ribbon pattern.”
The mistake to watch for
Mistaken answer: “The city grew steadily because the line always goes up.”
The line rises in every period, but the amounts differ: 15, 35 and 20 km². “Steadily” claims equal steps.
Correction: give the change for each period and say which is largest. Use “steadily” only if the changes are close to equal.
Self-check
1. Using City E, work out the percentage change from 1990 to 2000.
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15 ÷ 40 = 0.375, so 37.5%.2. And from 2010 to 2020?
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20 ÷ 90 = 0.2222, so 22.2%.3. In which period was the absolute change largest and in which was the percentage change largest?
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Both were largest in 2000 to 2010: 35 km² and 63.6%, compared with 15 km² and 37.5%, and 20 km² and 22.2%.Where does this lead next?
Growth figures are a kind of average over a whole city, so the next lesson asks what an average can hide. Continue with distinguishing an average from a distribution.
Earlier work on comparing settlement functions helps explain why growth takes place. If percentage change keeps tripping you up, an assigned teacher can go through your working step by step in IGCSE Geography one-to-one tuition.