Cambridge Syllabus Notes

📊 16. Graphs and Charts

Why Use Graphs?

Graphs turn raw numbers into visual stories. They help you spot patterns, compare values, and remember information faster. Think of a graph as a map that shows you where the data points are and how they move.

Types of Graphs

Graph Type	Data Best Suited	Example	When to Use
Bar Chart	Categorical data (e.g., number of students in each year)	📚 12 students in Year 1, 15 in Year 2, 10 in Year 3	When you want to compare whole numbers side‑by‑side.
Pie Chart	Part‑of‑a‑whole data (percentages)	🍕 40% pizza, 30% salad, 30% drink	When you want to show how each part contributes to the total.
Line Graph	Continuous data over time (e.g., temperature each day)	📈 20°C, 22°C, 19°C, 25°C over four days	When you need to show trends or changes.
Scatter Plot	Two quantitative variables (e.g., height vs. weight)	📊 Points plotted on an X‑Y grid	When you want to see if two variables are related.
Histogram	Distribution of a single quantitative variable	📉 Frequency of test scores	When you need to show how data is spread out.

Choosing the Right Graph

Identify the data type: categorical or quantitative.
Ask what you want to show:
- Comparison of categories? → Bar chart.
- Parts of a whole? → Pie chart.
- Trend over time? → Line graph.
- Relationship between two numbers? → Scatter plot.
- Distribution of a single variable? → Histogram.
Check the audience: Keep it simple for quick understanding.
Remember the rule: No more than 4–5 categories in a bar or pie chart to avoid clutter.

Examples & Analogies

Bar Chart: Like a stack of books where each book’s height shows how many students are in that year.
Pie Chart: Imagine a pizza sliced into pieces; each slice is a different subject’s share of total study time.
Line Graph: Think of a roller coaster track – the ups and downs show how grades changed each term.
Scatter Plot: Picture stars in the night sky; each star’s position tells you how two variables (e.g., hours studied vs. marks) relate.
Histogram: Like a bar code where each bar’s height shows how many people scored within a score range.

Exam Tips

Tip 1: Read the question carefully – it often hints at the best graph type.
Tip 2: Label axes clearly. For line graphs, include units (e.g., °C, days).
Tip 3: Use consistent colours across similar graphs to help the examiner follow your logic.
Tip 4: If you’re unsure, choose a bar chart for categorical data; it’s usually safe.
Tip 5: Practice drawing each type from raw data – the more you practise, the faster you’ll recognise the right choice in the exam.

Quick Decision Flow:

Is the data categorical? → Bar chart.
Is it a percentage of a whole? → Pie chart.
Is it a trend over time? → Line graph.
Is it a relationship between two numbers? → Scatter plot.
Is it a distribution? → Histogram.

Be able to select the graph or chart type