Seeing the Data
A well-chosen graph reveals patterns that a table of numbers hides. Data visualisation matches the data type to the right display so shape, trend, relationship, and outliers become visible at a glance.
Here are the core chart types and their purposes:
| Chart Type | Purpose & Structure |
|---|---|
| Histogram | Distribution of a single numerical variable using touching bars. |
| Bar chart | Compares values across categories using separated bars. |
| Scatter plot | Relationship between two numerical variables via plotted pairs. |
| Line chart | Trends of a value over an ordered sequence, usually time. |
| Box plot | Summarises a distribution via five numbers to compare groups. |
Chart Distinctions & Pitfalls
The crucial distinction is between a histogram and a bar chart, which look similar but display different data types.
| Feature | Histogram | Bar Chart |
|---|---|---|
| Data type | Continuous numerical | Categorical groups |
| X-axis | Number line (binned intervals) | Distinct labels |
| Bar spacing | Bars touch | Bars have gaps |
Common pitfall: Using a bar chart for continuous data or a histogram for categories. They answer different questions; mixing them up misrepresents the data.
Good visualisation requires honest design: a truthful axis starting at zero for bar heights, no distorting 3D effects, and a scale that neither exaggerates nor flattens real differences.