Cambridge IGCSE ICT (0417): Graphs and charts – Study Guide

A graph or chart turns a table of figures into a picture, so that patterns are easy to see. Cambridge IGCSE ICT 0417 expects you to create a suitable chart from spreadsheet data, label it fully and edit it to meet instructions. Marks in the practical paper come from choosing the right type, selecting the right data, adding every label that is asked for and making the result readable.

Where this fits in the specification

Graphs and charts are a practical skill that draws on spreadsheet work (the data and formulas), layout (placing the chart in a document or report) and audience (a chart for managers should be clear and formal, one for children bright and simple). Charts are often pasted into a word-processed report, so you also need to resize and place the chart correctly.

Create, label and edit a graph or chart

Choosing the chart type

Chart type	Best used for	Example
Bar or column chart	Comparing separate categories	Number of pupils in each year group
Line graph	Showing change over time or a trend	Monthly rainfall over a year
Pie chart	Showing parts of a whole as shares (percentages)	Share of sales by product
Scatter graph	Showing whether two sets of numbers are related	Height against shoe size

Use a pie chart only when the numbers add up to a meaningful whole and there are few categories (about six or fewer). Use a line graph only when the horizontal axis is ordered, like time. A common error is drawing a line through categories that have no order, such as different fruit.

Selecting the data

Before creating the chart, select exactly the cells needed, including the row and column headings, so that the labels and the legend are picked up automatically. Do not include a Total row or column unless asked, because it will appear as a category and distort the chart. If the data to chart is not next to each other, select the first block and hold down the control key to add the second.

You may need to decide whether the data series are in rows or in columns. Each data series is one set of values, shown as one line or one set of bars.

Labels to add

Examiners and tasks usually ask for these, and each is a separate mark:

• Chart title: says what the chart shows.
• Axis titles: on the horizontal (category, or x) axis and the vertical (value, or y) axis, with units where they apply, such as “Sales (thousands of dollars)”.
• Legend: needed when there is more than one data series, to show what each colour or line is. For a single series it may be removed to save space, if asked.
• Data labels: the actual values (or percentages for a pie chart) shown on the bars, points or sectors.
• Category labels: the names along the horizontal axis.
• Gridlines: optional lines that help read values.

Editing a chart

• Change the scale of the value axis, for example minimum 0, maximum 100 and major unit 20. Starting a bar chart’s axis above zero can mislead the reader.
• Change colours and fills, line styles and marker shapes. Choose colours that can be told apart, including in black and white print. Pie sectors often need different shading or patterns.
• Change the font and size of titles and labels for readability.
• Change the chart type if the first choice was not suitable.
• Resize and move the chart, and place it within the page margins when it is in a document.
• Add a secondary axis when two series have very different scales, for example sales in thousands and profit as a percentage.
• Edit the data in the spreadsheet; a linked chart updates automatically.
• For a pie chart, explode (pull out) a sector to emphasise it, if requested.

Worked example: a pie chart

A shop’s sales for a week, in items sold, are: Books 120, Games 90, Music 60, Toys 30.

Total = 120 + 90 + 60 + 30 = 300.

Category	Items	Percentage of total	Angle of sector
Books	120	120 / 300 = 40%	0.40 x 360 = 144 degrees
Games	90	90 / 300 = 30%	108 degrees
Music	60	60 / 300 = 20%	72 degrees
Toys	30	30 / 300 = 10%	36 degrees

Check: percentages add to 100% and angles add to 144 + 108 + 72 + 36 = 360 degrees. Spreadsheet software will calculate the angles for you, so you need to select the Category and Items columns (not the Total), give the chart the title “Weekly sales by category”, and show the percentage data labels with a legend. If the Total had been included, it would have appeared as a huge sector of 300 items and made the others look tiny.

Worked example: a line graph with two series

A school records the temperature at noon on five days in two classrooms:

Day	Mon	Tue	Wed	Thu	Fri
Room A (degrees Celsius)	19	21	22	20	18
Room B (degrees Celsius)	23	24	26	25	22

A line graph is suitable because the days are in order. There are two series, so a legend is needed. The vertical axis could run from 15 to 30 with a unit of 5, titled “Temperature (degrees Celsius)”, and the horizontal axis titled “Day of the week”. The graph shows that Room B is warmer on every day, by 4 degrees on Monday (23 - 19) and 4 degrees on Friday (22 - 18). The pattern in both rooms is to rise to Wednesday then fall.

When you give an interpretation, quote a figure and a trend, as in this example, instead of saying only “Room B is hotter”.

Placing a chart in a document

Copy the chart and paste it into the report, then use the same techniques as for images: size it so that it does not distort, place it within the margins, set the text wrapping, and add a caption if needed. Remember that a chart should be readable at the final size, so check the font and labels in print preview.

Common mistakes

• Using the wrong type of chart, such as a pie chart for change over time.
• Including the Total row or column in the selected data.
• Missing one or more labels, such as a chart title, an axis title or the unit.
• Leaving the legend out when there are two or more series, or leaving a pointless legend on a single series chart.
• Using similar colours that cannot be distinguished.
• Starting the vertical axis at a number other than zero for a bar chart, which exaggerates differences.
• Stretching a chart when resizing so that the text becomes distorted.

Exam technique

Read the task for exactly which data to chart, which type to use and which labels to add, then tick each off after creating the chart. In theory questions, justify the choice of a chart by linking its purpose to the data (“a line graph is suitable because the data changes over time”). For describe the trend questions, state the direction and quote values.

Check your understanding

1. Which chart type best shows a change in temperature during a day? A line graph.
2. Which chart shows each product’s share of total sales? A pie chart.
3. State three labels that a chart should normally have. Chart title, axis titles and a legend (or data labels).
4. Why should the Total row not be included in a pie chart? It would be shown as a category of its own and distort the sectors.
5. Items sold are 45, 30 and 15. Calculate the angle of the first sector in a pie chart. 45 / 90 x 360 = 180 degrees.
6. When is a legend needed? When a chart has more than one data series.
7. Why might a secondary axis be added to a chart? When two series have very different scales, so both can be read clearly.
8. Give one problem with starting a bar chart’s axis at 50 and not 0. It exaggerates the differences between bars and can mislead the reader.

Frequently asked questions

Which chart should you use in IGCSE ICT? In Cambridge IGCSE ICT (0417), use a bar or column chart to compare separate categories, a line graph to show change over time, a pie chart to show parts of a whole, and a scatter graph to show whether two sets of numbers are related.

Why should you not include the Total row in a chart? A Total row or column would be plotted as a category of its own and distort the chart, so select only the data and headings needed unless the task says otherwise.

When does a chart need a legend? A legend is needed when a chart has more than one data series, to show what each colour or line represents. For a single series it may be removed if the task asks.

Why should a bar chart’s value axis start at zero? Starting the vertical axis above zero exaggerates the differences between bars and can mislead the reader, so a bar chart normally starts at zero unless the task sets a different scale.