Building number confidence: Graphical data
4. Charts and graphs
4.2. Bar chart
Also known as a column chart, a bar chart represents data using vertical bars, which enable a quick comparison of values across different categories.
The categories are displayed horizontally along the bottom of the chart (the x axis), with a vertical value scale on the left (the y axis).
Data labels can be added to each vertical bar to provide exact figures, however keeping it simple, as in this example, gives an immediate picture of how things are.
A legend below the chart names the category represented by each colour.
Data from: Daily sales table.
| Americano | Latte | Flat white | Cappuccino | Tea | |
|---|---|---|---|---|---|
| Monday | 76 | 14 | 20 | 12 | 35 |
| Tuesday | 60 | 30 | 14 | 25 | 17 |
| Wednesday | 57 | 28 | 30 | 22 | 25 |
| Thursday | 37 | 32 | 12 | 27 | 14 |
| Friday | 70 | 36 | 18 | 32 | 28 |
| Saturday | 72 | 35 | 27 | 16 | 32 |
| Sunday | 55 | 25 | 23 | 27 | 40 |
Looking at the daily sales of coffee and tea from the previous page, for example, we can see at a glance that in this cafe, Americano is the most popular coffee.
Data check
What was the second most popular drink on Sunday?
Tea had the second highest volume of sales on Sunday, which in this case we can read as 40, because the bar touches the horizontal line representing this value. Other categories are not so easy to read and without data labels would have to be estimated, but we still have a quick visual representation for each, which is the main purpose of this chart.
Stacked column chart
A stacked column chart displays categories, over time, as part of a whole. The daily sales report in this format has one column for each day of the week, with the volume of sales for each category stacked within these.
Visually, we can still see that sales of Americano outstrip other options, but without data labels, totals for each have to be estimated. However, the stacked chart does show us that Friday had the highest sales in total, with sales on Saturday very slightly behind.
Data check
Which day had the least total sales?
Thursday had the least number of sales. The stacked bar reaches to slightly above the 120 sales mark.