Building number confidence: Graphical data

4. Charts and graphs

4.3. Line graph

A line graph, or line chart, uses straight lines to connect data points, to show trends and relationships in data over time or categories.

This example shows data collected over a week, but a similar chart could be used to show trends over months or years.

A legend below the chart names the category represented by each colour.

Coloured lines connecting data points show trend in sales for various categories over a week.

Data from: .

  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

Markers can be included to show the data values used to create the chart.

Line chart showing data (with data markers) and trends over time.

Multiple data series can appear very busy, making the trend information less of a focus. Line charts are most powerful, visually, when only one or two data sets are plotted.

Line graph with only 2 data sets which makes it easier to highlight the differences between them.

 

 Data check

Looking at the line chart (above) comparing sales of teas and Americanos, which day has the lowest sales of both?

Thursday has the lowest sales in both categories. For Americano, sales dip below 40, and tea sales are less than 20.