Types of Graphs
Discover when and how to use bar graphs, line graphs, pie charts, stem-and-leaf plots, and dot plots to display data.
Bar Graphs and Line Graphs
Bar Graph
Uses rectangular bars to compare categories. Bars can be vertical or horizontal.
Best for: Comparing groups or categories
Favourite Sports
Line Graph
Connects points with lines to show how a value changes over time.
Best for: Showing trends over time
Temperature over Months
Pie Charts and Dot Plots
Pie Chart
A circle divided into slices to show proportions. Each slice represents a percentage of the total.
Best for: Showing how a whole is divided into parts
Dot Plot
Shows each data value as a dot above a number line. Easy to see the distribution and spread of small data sets.
Best for: Small data sets, spotting clusters and outliers
Number of siblings
Stem-and-Leaf Plots
A stem-and-leaf plot displays numerical data where the tens digit forms the "stem" and the units digit forms the "leaf". It preserves all the original data values while showing the distribution.
Data: 23, 27, 31, 35, 35, 38, 42, 46, 51
How to Read It
- Each row shares a stem (tens digit).
- Each leaf is the units digit of each value.
- The row starting with 3 shows 31, 35, 35, 38.
- You can quickly see that values cluster in the 30s.
Best for: Numerical data, seeing shape and spread, finding median
Choosing the Right Graph
| Graph Type | Best Used For | Data Type |
|---|---|---|
| Bar Graph | Comparing categories | Categorical |
| Line Graph | Trends over time | Numerical (continuous) |
| Pie Chart | Parts of a whole | Categorical (proportions) |
| Stem-and-Leaf | Distribution, all values visible | Numerical (discrete) |
| Dot Plot | Small data sets, clusters | Numerical (small sets) |
Key Vocabulary
Distribution
How data values are spread out across the range in a data set.
Outlier
A data value that is much higher or lower than most other values in the set.
Scale
The numbered intervals along an axis of a graph that show the values being represented.
Sector
A slice of a pie chart, where the size of the angle represents the proportion of the total.
Worked Examples
Which graph best displays the change in Australia's population from 2010 to 2025?
A line graph is best because it shows how the population changes over time, making trends easy to read.
A class recorded these test scores: 62, 65, 67, 71, 73, 75, 75, 82, 88. Create a stem-and-leaf plot.
In a pie chart, a sector representing "Transport by car" is 30% of the whole. What angle does this sector have?
A full circle = 360°
Angle = 30% × 360° = 0.30 × 360 = 108°
Knowledge Check
Select the correct answer for each question.
Question 1
Which type of graph is best for comparing the number of students in each year group at a school?
Question 2
In a stem-and-leaf plot, the row "4 | 2 5 8" represents which values?
Question 3
A pie chart shows that 25% of students walk to school. What angle does this sector have?
Question 4
Which graph would best show the daily maximum temperature in Sydney over one month?
Question 5
A dot plot showing 10 values has dots at: 3, 3, 4, 4, 4, 5, 5, 6, 6, 8. What is the most common value (mode)?
Key Concepts Summary
- ●Bar graphs compare categories; line graphs show trends over time.
- ●Pie charts show proportions of a whole. Sector angle = percentage × 360°.
- ●Stem-and-leaf plots preserve all data values and show the distribution clearly.
- ●Dot plots are ideal for small data sets to reveal clusters and outliers.
- ●Always choose the graph type that best suits the data type and the question being answered.