A combined graph carries two sets of data at once, so every reading starts with one question: which axis does this mark belong to? Get that right and the rest is ordinary reading.
The lesson belongs to graphs and photographic interpretation. If you are unsure when to draw one, see choosing a graph type.
What is the reading routine?
Use four steps every time, in this order.
- Read the title and the two vertical axis labels, with units.
- Match each series to its axis: bars to one side, line to the other.
- Read values off the correct scale and write the unit.
- Describe the pattern, then compare the two patterns.
The order matters because skipping step 2 is the easiest way to mix up the axes.
Worked example: an original dataset for Town R
An original graph for Town R shows rainfall as bars on the left axis (0 to 400 mm) and mean temperature as a line on the right axis (20 to 32 °C). The bars peak in December at 360 mm and fall to 70 mm in July. The line reads 26 °C in December and 29 °C in July.
Question: “Describe the relationship between rainfall and temperature in Town R.”
A full answer reads: “Rainfall is highest in December at about 360 mm and lowest in July at about 70 mm. Temperature is lowest in December at 26 °C and highest in July at 29 °C. The wettest month has the lowest temperature, and the driest month has the highest temperature, so the two patterns move in opposite directions.”
Notice that each value has its unit, each value comes from its own axis, and the last sentence compares without claiming a cause.
The mistake: reading the line on the bar axis
The line at its July peak sits near the top of the graph, so a rushed reader reads it on the left scale and writes “temperature is about 300”. That is a rainfall scale, and the answer is wrong by more than a factor of ten.
| Step | Wrong reading | Right reading |
|---|---|---|
| Axis used | Left axis for the line | Right axis for the line |
| Value written | 300 | 29 °C |
| Unit | None | °C |
The fix is to trace a finger from the line across to the right-hand axis before writing any number.
Check yourself
In the Town R graph, rainfall in March is the bar reaching the 200 line on the left axis, and temperature in March is the line point halfway between 26 and 30 on the right axis. State both values with units.
Answer
Rainfall is 200 mm, read on the left axis for the bars.
Halfway between 26 and 30 is 28, so temperature is 28 °C, read on the right axis for the line.
What to study next
Practise reading and writing on a fresh dataset with the graph evidence and fair-comparison lab, then see how photographs are read in separating visible evidence from speculation.
For a teacher who checks every reading against your working, see online one-to-one Geography tuition.