Line graphs and data displays
You've already met bar charts, tally charts and pictograms in earlier years. In Year 5 we add three more useful displays:
- Line graphs — for showing how something changes over time.
- Line plots — for showing many measurements on one number line, often with fractions.
- Double bar graphs — for comparing two related sets of bars side by side.
Each kind of display has its own job. Picking the right one for the data is a skill in itself.
Line graph
A line graph has two axes — usually time on the bottom (days, months, hours) and a quantity on the side (temperature, number of visitors, plant height). Each measurement is a single point, and the points are joined with straight lines. The line shows the trend: going up, going down, or staying level.
How to read a value
Pick the day on the bottom axis. Trace a finger straight up to the line. Then trace straight left to the number line on the side. That number is the value on that day.
Spotting trends
- Line going up = the quantity is growing.
- Line going down = it is shrinking.
- Line going flat = staying the same.
- A sudden jump between two points means a big change between those two times.
When to use a line graph
Line graphs are best for data over time. Don't use them for unrelated categories — e.g. "favourite ice-cream flavours" doesn't have an order, so connecting the points with a line would suggest a fake trend.
Line plot
A line plot (also called a "dot plot") shows many measurements at once, stacked above a number line. Each × represents one measurement.
Line plots are common with fraction data. You measured the lengths of nine pencils to the nearest quarter-inch — every measurement gets one ×. Stacks of × marks show repeats (here, three pencils were 1/2 inch).
What questions can a line plot answer?
- What's the most common value? (The tallest stack.)
- What's the largest value? The smallest? (Look at the far right / far left.)
- What's the range? (Largest − smallest. This is the question the line-plot exercise asks.)
- How many measurements in total? (Count all the × marks.)
Double bar graph
A double bar graph shows two related sets of bars side by side. It is great when you want to compare the same thing in two situations — for example, number of boys vs number of girls in each of four classes.
The legend (key) tells you which colour belongs to which series.
Reading a double bar graph
- For one bar: trace from the top of the bar to the y-axis to read its value.
- To compare two bars in the same group: read both, then subtract.
- To find the difference between two series in a group: compute |valueA − valueB|.
This is what the double bar graph exercise asks: pick the highlighted group, read both bars, subtract.
Picking the right display
| You want to show… | Best display |
| How something changes over time | Line graph |
| Many measurements (especially fractions) | Line plot |
| Two related categories across groups | Double bar graph |
| One category across groups | Bar chart |
| Frequencies in a long list | Tally chart |
| Counts using picture symbols | Pictograph |