visualising-data-course

Visual Grammar

This section describes how visual attributes relate to the characteristics of the data.

Each chart plots a set of variables

Bar chart: (1-2 categorical, 1 continuous)

• Axis: categorical
• Bar Length: continuous (optional)
• optional colour legend: categorical (fewer items)

Scatter plot: (2 continuous, 1-3 categorical)

• x-axis: continuous
• y-axis: continuous
• Optional categorical variables: for colour, shape, or size encoding

Example: (stacked) bar chart

What are the categorical and continuous variables?

Example: Scatter plot

What are the categorical and continuous variables?

Reading a chart: look at the anatomy

Scaffolding provides the scope and indicates the reason, purpose.

• Chart title - purpose of the chart
• Axes - what do they measure? are these labelled clearly? Choice of start and end points?
• Sources of data: are they shown, trustworthy

Visual encoding translates quantities to marks and symbols

• position , length, slope, angle ,colour (hue and shade),area
• Less often used: shape, pattern, line thickness

Context (author,intended audience, location of report)

Grammar of Graphics

• data geometries are the basic configuration of the chart e.g. line, column
• aesthetics map visual attributes (x, y, colour, shape, fill, alpha) to dataset columns.
• scales configure the axes and set ranges, limits on visual attributes
• stats summarise the data before plotting, most obviously in box plots
• facets - small multiple charts

Source: ggplot2 (ggplot2-book.org) Hadley Wickham