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: 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

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.