The conventional interface to graphics is like a sentence:

But different types of graphics are often combined, e.g.:

• scatterplot, with groups connected
• heatmap, with dendrogram
• barchart, with error bars

• Frame
• Layer
• Glyph
• Guide
• Facet
• Scale
• Annotation
• Transform
• Statistic

A glyph is a graphical element that conveys information:

A piece of two-dimensional space.

• Defined by two variables.

The variables can be either quantitative, categorical, or ordinal.

A guide helps the human reader of a chart to ascertain the value of a variable for each case.

\(x\)- and \(y\)- axis are usual.

• The number line is ordered.
• Quantitative variables have a natural order.
• Categorical variables do not. So an order must be specified.
  • Alphabetical is often used, but not often useful.

• Color
• Size
• Shape
• Transparency

These are graphical attributes reflected in glyphs. The guide tells you how the attribute is related to the value or level of the corresponding variable.

A guide is the displayed manifestation of a scale. The scale translates the variable into a graphical attribute.

Let's add some new data in a new layer: the shape of states.

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