Reading charts

When a visualisation designer creates a visualisation, they select the most appropriate chart type. They will then display the data using visual marks, attributes and chart apparatus to make a visualisation that is easy to read.

Marks and attributes

Marks are things like bars, shapes, lines and dots. Attributes are the properties of these marks such as size, colour, position and angle. These combinations of marks and attributes form the basis of charts.

When we read charts or graphs our task is to learn what the various marks, shapes, lines, patterns and colours mean: What is big? What is small? Which category does that colour represent? Is that value above average?

Chart apparatus

There will often be several different types of chart apparatus to assist us in reading a chart:

• Axis lines with labeled scales and gridlines help us to judge the values of properties like bar lengths and line position
• Legends and keys help us to understand the links between different colours, shapes or sizes
• A map layer helps us to understand the locations in geographical displays
• Visual guides such as reference lines, drop lines or shaded backgrounds further help us to understand significant features of the data

More about making visualisations

You can find out more about the process of making visualisations by watching the video How a visualisation is made at seeingdata.org.