Line graphs, bar charts and histograms

Graphs are a useful way to show numerical data. There are a variety of graphs that can help highlight patterns and be used to reach conclusions. Choosing the right graph is very important.

Exploring a range of graphs and their uses

Line graphs

Primary industries have declined since pre-industrial times. Secondary industries peaked in industrial times. Tertiary industries have increased. Quaternary industries have only appeared recently.

Line graphs show how data changes over time or space. The x-axis shows time or distance.

A line graph could be used to show the changes in a country's employment structure over time. This graph shows that in the post-industrial era approximately 11% of employed people work in primary industries, 31% in secondary industries, 54% in tertiary industries and 4% work in quaternary industries. Note how the total adds up to 100%.

Bar charts

Bar charts show grouped data as rectangular bars, eg the number of tourists visiting a resort each month. Divided bar charts split up each rectangular bar to break the information down further. A divided bar chart could be used to show the age breakdown of tourists visiting a resort.

A bar chart shows a single value per bar, eg number of tourists per month. A divided bar chart divides the bar into differently coloured sections. A key provides further breakdown of the data.

Population pyramids are bar charts that show how many people of different ages are living in a place or country. Population pyramids show the bars arranged sideways, rather than upwards. The x-axis shows the number of people, the y-axis shows their ages. The bars on the left show the number of males and the bars on the right show the number of females.

The UK's population pyramid has most people in the 30-39 age range, with number decreasing sharply after 55.

Bar charts and line graphs can be combined. Climate graphs are an example of this. The x-axis shows the months of the year and there are two y-axes to show average temperature and total rainfall. The temperature is shown as a line and the rainfall as bars.

The UK's average temperature peaks in July and August at 23°C. Rainfall happens all year round, peaking in October at 63 mm.

Histograms

Histograms are similar to bar charts, but they show frequencies rather than groups of data. A histogram could be used to show frequencies of earthquakes of each magnitude on the Richter scale.

A histogram shows bars next to each other with no gap between them. The height of the bar indicated the frequency of the data, eg number of earthquakes per magnitude.