A sourced case is a real example whose facts carry a place, a date, a source and a stated limit. Exam answers that use such a case read as evidence, not opinion.
This lesson follows comparing a hard and a soft management mechanism, and it is the fourth step in coasts and marine processes.
What goes into a case ledger?
For every fact, keep four things.
- Place: the exact stretch of coast, not just the country.
- Date: the year or period the fact applies to.
- Source: who produced it, such as a government agency, a university report or a textbook.
- Limit: what the fact cannot tell you, such as the small number of survey dates.
The Geography evidence and case-study ledger is built for this. This site does not supply real case data for you, so the example below is invented.
Worked example
“Example Bay” is a made-up place. A survey in 2005 measured the cliff edge at 40.0 m from a fixed marker. A survey in 2015 measured it at 16.0 m from the same marker.
Step 1, change: 40.0 − 16.0 = 24.0 m of cliff-top retreat.
Step 2, period: 2015 − 2005 = 10 years.
Step 3, rate: 24.0 ÷ 10 = 2.4 m per year on average.
Step 4, record the limits: there are only two surveys. Retreat may have been fast in some years and slow in others, and the average hides that.
Step 5, write it safely: “Between the 2005 and 2015 surveys, the cliff edge at Example Bay retreated by 24.0 m, an average of 2.4 m per year. Only two dates were measured, so the yearly pattern is not known.”
The mistake to watch for
A common slip is to extend an average into the future as if it were certain.
Over-claim: “At 2.4 m a year, the road 50 m back will be gone in 20 years.”
2.4 × 20 = 48 m, so the sum is right, but the statement treats the rate as fixed.
Write instead: “If the same average rate continued, about 48 m would be lost in 20 years, but the rate may change with storms or management.” The calculation stays, and the limit is stated.
Check yourself
1. A cliff edge is 30.0 m from a marker in 2010 and 21.0 m in 2020 (invented). Find the average yearly retreat.
Show answer
30.0 − 21.0 = 9.0 m over 10 years, so 0.9 m per year.
2. Which of these is missing from “The cliffs there are retreating fast”? Place, date, source or limit?
Show answer
All four. There is no exact place, no date, no source and no figure or limit.
3. Why should an answer say “in the 2020 survey” and not “now”?
Show answer
The survey describes the coast on that date only, and conditions may have changed since.
Where this leads next
The last lesson applies this care to one particular claim, in avoiding the claim that a real site is currently safe.
If you want help turning a case study into a short, source-aware answer, our teachers in online one-to-one Geography tuition can work through your own notes. The statistics and distribution explorer helps with averages.