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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.

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.

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.

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.

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.

Pie charts

Pie charts show percentages as a circle divided into segments. A pie chart could be used to show how students travel to school. Each piece of data is shown as a proportion of 360, because there are 360 degrees in a circle. If 25 out of 100 students travel to school by car, the angle is worked out using the calculation: (25 ÷ 100) × 360 = 90 degrees.

Scatter graphs

Scatter graphs show relationships between two sets of data. Points are located using the x and y-axis. Sometimes these points are arranged in a pattern. A scatter graph could be used to show how literacy is related to GDP.

A line of best fit helps to show correlations, or patterns within the data. The line of best fit runs through the middle of a collection of points on the graph, ideally with an equal number of points on either side of the line.

• A strong correlation is when the points are very close to the line of best fit.

• A weak correlation is when the points are far away from the line of best fit.

• A positive correlation is when an increase in one factor is mirrored by an increase in another (the line of best fit goes from the bottom left to the top right).

• A negative correlation is when an increase in one factor is mirrored by a decrease in another (the line of best fit goes from the top left to the bottom right).

Proportional symbols, pictograms and cross sections

Proportional symbols can be added to maps or graphs to show information about different places. The graph below plotslife expectancy against income for each country. It also shows population size. Each country is shown as a circle where the size of the circle is proportional to the population of the country, ie the bigger the circle, the bigger the population of that country.

Pictograms are like bar charts, but they use small pictures or icons to show data instead of bars. Pictograms could be used to show the weather conditions experienced in a particular place over a period of time.

Cross sections are line graphs that show a sideways view of a landscape. They can show features such as hills and valleys, or depths, such as the depth of a river. Cross sections of hills use contour lines to determine the height of the land. Cross sections of river depths are drawn using negative numbers so that the line graph looks like depth, rather than height.

Radial/radar graphs

Radial/radar graphs are sometimes called rose charts. They have a central point from which data radiates outwards. This data can be plotted as points along a line, where all points are joined up to form a shape. It could also be plotted as segments along a line. Wind speed and direction is often shown as a radial graph. Radial graphs can show lots of different data and do not have to involve compass points.

Some data is easier to understand when it is shown on a map. This is especially true of spatial data, where the spread of the information is important.

Choropleth maps

Choropleth maps show interval data (data that is linked, rather than data from different categories) as colours. They are shaded in using one colour, where the darker shades represent high numbers and the lighter shades represent low numbers. A choropleth map needs a key to explain what the different shades mean. Spatial population density can be shown using a choropleth map.

Isoline maps

Isoline maps show lines that join up areas or values that are equal. Atmospheric pressure is shown using an isoline map. The areas of equal pressure (isobars) are joined using a line, which helps people to see the position of high and low-pressure systems. Contour lines are also isolines which show height above sea level.

Dot maps

Dot maps show information as individual dots on a map. Each dot might represent more than one of something. Dot maps are often used to show population distribution.

Desire lines and flow lines

Desire and flow line maps show movements from one place to another:

• flow lines show the exact path of movement

• desire lines show a general direction of movement

Movements are shown as lines. Thick lines show high amounts of movement and thin lines show low amounts.Trade or migration patterns are often shown using desire or flow lines.

Proportional symbols

Proportional symbols can be added to a map to show differences between places. The same symbol appears larger or smaller, depending on how something changes. Proportional symbols on maps could be used to show the number of wind farms within a country.

Describing and explaining a graph

Very often students will be asked to demonstrate their understanding of a graph and what they are really being asked to do is to describe and/or to explain what the graph shows.

Describing a graph

If asked to describe, students have to put into words what is shown on the graph, but it's not necessary to provide any reasons for what the graph is showing.

What students will have to do is to show that they understand the key and can describe the map.

Look at the mark allocation before deciding how much detail needs to be include in the description. For example, in the Proportional Symbol map (above) showing windfarms, it might be described by saying:

• This map shows that wind energy is generated all over Great Britain, but there is more of it onshore in Scotland where there are two windfarms with between 201 and 350Mw of electricity generated.
• There are also many smaller plants in Scotland, but most are generating between 26 and 50Mw, particularly in the Southern Uplands.
• In England, on the other hand, there are many small windfarms generating 10Mw, particularly along the Pennines. However, England has the largest windfarm, off the coast of East Anglia, which is generating more than 350Mw of electricity.

Explaining a graph

If also asked to explain the graph, students need to suggest plausible reasons for the patterns they have described. In this case, it might be to do with:

• shallow seas off SE England in which it is convenient to build offshore wind turbines
• high mountains in Scotland with few people living nearby making that area ideal for large windfarms.

The exam will only ask candidates to explain a graph which shows something they will be familiar with from their Geography GCSE course.