GCSE

# Graphs

## 1. Graphs

### Data

Quantitative data records quantities (e.g. numbers, sizes, frequencies).

Qualitative data records subjective qualities (e.g. opinions and attitudes).

Discrete data can only take certain values (e.g. whole numbers)

Continuous data can take any value (e.g. length, width, time)

### Justifying your choice of data presentation

Your findings can be presented with a range of graphical and mapping techniques. Each form of data presentation needs to be justified. Here is an example.

 Fieldwork technique Systematic sampling along a transect from the PLVI to the edge of the CBD. An environmental quality score was calculated at every 30 metres. Data presentation Line graph with distance from PLVI on x-axis and environmental quality score on y-axis. Points were joined up Bad justification The line graph shows how environmental quality changes as distance increases from the PLVI. Good justification A line graph is appropriate because both distance from the PLVI and environmental quality core are numerical. The points were joined up because distance is continuous data.

### Bar charts

Bar charts are use to show the numbers of things (or frequency) in several categories

• Plot the categories on the x-axis
• Leave gaps between the bars as data are not continuous (called discrete data)

### Divided bar charts

Divided bar charts are used to show the frequency in several categories, like ordinary bar charts. It is a type of compound bar chart. But unlike ordinary bar charts, each category is subdivided.

• Plot the categories on the x-axis
• Leave gaps between the bars as data are discrete data
• Use colours or shading to show the subdivided categories, and include a key

### Percentage bar charts

Percentage bar charts are use to show the percentage of each subdivision in several categories. It is a type of compound bar chart.

• Plot the categories on the x-axis
• Leave gaps between the bars as data are discrete data
• Use colours or shading to show the subdivided categories, and include a key
• Each bar should be the same height (i.e. 100%) Example of a percentage bar chart, using the same data as the divided bar chart above.

### Histograms

Histograms are used to show the numbers of things (or frequency) along a continuous scale

• Plot the sliding scale on the x-axis
• Do not leave gaps between the bars as data are continuous data

### Pie charts

A pie chart is a circle divided into sectors. Each sector represents a percentage.

• Sectors can be shaded or coloured, and need labels or a key
• Multiple pie charts can be used where the size of each circle shows ratio.

### Line graphs

• Both axes are numerical.
• If time is one of the variables, always plot it on the x-axis.
• Only join up the points if the data are continuous. Example of a line graph: the points are joined as the x-axis is continuous. A river channel profile: an unusual line graph.

### Scatter graphs

• This needs one independent variable (on x-axis) and one dependent variable (on y-axis).
• Both axes must show continuous data.
• Do not join up each point, but use a line of best fit instead.