A line graph shows how a quantity changes over time. Individual data points are plotted on a grid and then joined with straight lines. The horizontal axis (x-axis) shows time (months, years, hours) and the vertical axis (y-axis) shows the measured value.
Line graph = data points plotted and joined with straight lines — shows change over time
Example 1 — Reading a value from a line graph
Step 1
Identify the axes. The x-axis shows months; the y-axis shows temperature in °C.
Step 2
To read July: find Jul on the x-axis, trace straight up to the plotted point, then read across to the y-axis → 22°C.
Step 3
To find the range: maximum (Jul) = 22°C, minimum (Jan/Dec) = 4°C. Range = 22 − 4 = 18°C.
Example 2 — Describing the trend
Step 1
Look at the overall direction of the line from left to right. Rising = upward trend. Falling = downward trend.
Step 2
The temperature rises from January to July (peak at 22°C), then falls from July to December.
Step 3
Write a sentence: "Temperature increases from January, peaks in July at 22°C, then decreases back to 4°C in December — showing a seasonal pattern."
Key exam words: "upward/downward trend", "overall increase/decrease", "peaked in [month]", "remained stable between [dates]", "fell sharply between [months]".
✓ Quick Check 1 — Trends and reading line graphs
Question 1 of 10
Drawing Line Graphs — Scale, Plotting, and Labels
Drawing an accurate line graph requires choosing a sensible, even scale for both axes. Every interval must represent the same value — you cannot change the scale partway up. Label both axes with titles and units, add a title, and join each consecutive pair of points with a straight line.
Steps: choose scale → label axes with units → plot each point → join with straight lines using a ruler → add title
Choose a y-axis scale: values range from 40 to 80 — use 0 to 90 in steps of 10. (Must include 0 and go above the maximum.)
Step 2
Label the x-axis "Day of the week" (Mon, Tue, Wed, Thu, Fri) and the y-axis "Number of customers". Add a title.
Step 3
Plot each point with a cross (×): Mon at 40, Tue at 55, Wed at 70, Thu at 65, Fri at 80.
Step 4
Join consecutive points with a ruler. Trend: overall increase with a slight dip on Thursday.
Common mistake: never change the y-axis scale halfway up the axis — every grid square must represent the same value. Also, always start at 0 unless told otherwise.
✓ Quick Check 2 — Drawing line graphs accurately
Question 1 of 10
Comparing Two Line Graphs on the Same Axes
Two data sets can be plotted on the same pair of axes using different coloured or styled lines. A key (legend) must label each line. This allows you to compare trends directly, identify when lines cross (crossover points), and state which is greater at any given time.
Example 4 — Reading a dual-line graph
Step 1
Use the key. The solid blue line is Shop A; the dashed yellow line is Shop B.
Step 2
Read January values: Shop A = 20, Shop B = 12. Shop A started with higher sales.
Step 3
Identify the crossover: the lines meet between February and March — this is where Shop B overtook Shop A briefly in March (both at approximately 15–18).
Step 4
In June: Shop A = 25, Shop B = 21. Shop A is £4,000 higher by June. Shop A recovered and pulled ahead.
Example 5 — Comparing trends
Step 1
Shop A trend: high start (20), dips to a low of 15 in March, then rises strongly to 25 in June. More variable.
Step 2
Shop B trend: starts lower (12) but rises steadily Jan–Apr, then levels off slightly. More consistent growth.
Step 3
Both shops end June higher than January, but Shop A shows greater fluctuation while Shop B shows steadier growth.
Always include a key when drawing a dual-line graph. Use different colours or line styles (solid vs dashed) and label each one in the key.
✓ Quick Check 3 — Dual-line graphs and comparison
Question 1 of 10
Practice: Reading Values from a Line Graph
A shop's monthly sales (£000s): Jan 12, Feb 18, Mar 24, Apr 20, May 28, Jun 32. Answer the questions below.
#
Question
Answer
Result
1
What were the sales in March? (£000s)
2
In which month were sales highest?
3
By how much did sales rise from January to June? (£000s)
4
Which month showed a dip (lower than the month before)?
5
What were the sales in January? (£000s)
6
What were the sales in May? (£000s)
7
By how much did sales rise from February to March? (£000s)
8
What were the total sales for January to March combined? (£000s)
9
By how much did sales rise from April to May? (£000s)
10
What were the total sales for April to June combined? (£000s)
⚠ Things to Watch Out For
Joining points with curves instead of straight lines: Connect consecutive data points with STRAIGHT LINES. Curved lines suggest continuous trend data, not discrete data points.
Wrong scale on y-axis: The y-axis scale must be consistent — equal spacing for equal value differences. An uneven scale distorts the visual impression of trends.
Not plotting points first: Always plot individual points (×) accurately before connecting them. Drawing a line without marking points leads to inaccurate graphs.
Interpolation beyond the data: Only interpolate (read values from the graph) BETWEEN plotted data points. Extending the line beyond the data range (extrapolation) gives uncertain estimates.
Misreading between gridlines: When reading a value between gridlines, estimate carefully. Each small square represents a specific value — count squares, don't guess.