Working with complex data and sources

At GCSE you will combine maps, statistics, photos and people's views. The skill is choosing good sources, calculating carefully and judging how far to trust each one.

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Using secondary data

Secondary data comes from other people. Useful sources include the census, Ordnance Survey maps, the Met Office, the Environment Agency and satellite images.
The census counts everyone in the country, usually every 10 years. The most recent census in England and Wales was on 21 March 2021; Scotland's was held in 2022.
In a GIS, different datasets can be layered on one map, such as flood zones on top of housing, so you can see where they overlap.

Useful calculations

Percentage: part / whole x 100.
Percentage change: (new value - old value) / old value x 100. A town growing from 40,000 to 50,000 people grew by 10,000 / 40,000 x 100 = 25%.
Density: amount / area, such as people per km2.
Rate per 1,000: used for birth and death rates.

Judging sources

Ask: Who made it? When? Why? Is it reliable (would it give the same result again)?
Official statistics and scientific sources are usually reliable; adverts, campaign groups or social media may be biased (one-sided).
Check the date: old data may be out of date. Check the sample size: a survey of 5 people is weaker than one of 500.
Using several sources that agree (triangulation) makes a conclusion stronger. Always say how certain you are.
Worked example

A village had 2,000 people in 2011 and 2,300 in 2021. Calculate the percentage change.

  1. Change = 2,300 - 2,000 = 300.
  2. Divide by the old value: 300 / 2,000 = 0.15.
  3. Multiply by 100: 15%.

Answer: A 15% increase.

Key idea

Secondary data includes the census (England and Wales, 21 March 2021), OS maps and Met Office data; GIS layers datasets. Percentage change = (new - old) / old x 100. Judge sources by who, when, why, reliability, bias and sample size; triangulate with several sources.

Key words
GIS
Geographical Information Systems: computer maps that show data in layers to reveal patterns.
Percentage change
Percentage change = (new value minus old value) / old value x 100.

All KS3 Geography key terms and definitions →

Quick check

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Extra practice

2 more questions

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  1. A town's population rose from 40,000 to 50,000. What was the percentage increase?

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    Answer: 25 %

    (50,000 − 40,000) ÷ 40,000 × 100 = 25%.

  2. Traffic counts fell from 400 to 300. What was the percentage decrease?

    Show the answer

    Answer: 25 %

    100 ÷ 400 × 100 = 25%.

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Sources and references

Checked by the GCSE-ready editorial team, 23 October 2026. Last updated 2 October 2026. Spotted a mistake? Tell us and we will fix it.

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