Graph Creation

Stages

Three stages of making a graph:

1. Specification
2. Assembly
3. Display

Specification

Statistical graphic specifications are expressed in six statements

• DATA: a set of data operations that create variables from datasets
• TRANS: variable transformations (e.g., rank)
• SCALE: scale transformations (e.g., log)
• COORD: a coordinate system (e.g., polar)
• ELEMENT: graphs (e.g., points) and their aesthetic attributes (e.g., color)
• GUIDE: one or more guides (axes, legends, etc.)

Assembly

Assembling a scene from a specification requires a variety of structures in order to index and link components with each other. One of the structures we can use is a network or a tree.

Display

Rendering the graphics. 

Syntax of the Grammar of Graphics

• Create Variables: to extract data into variables
• Apply Algebra: a graphics algebra consisting of three operators — cross, blend and nest — applied to a set of variables, together with a set of associated rules
• Apply Scales: A categorical scale transformation associates the values of a categorical variable with the set of integers
• Compute Statistics: do some statistics on the data
• Construct Geometry: the grammar of graphics has a variety of different geometric graphing operations
• Apply Coordinates: to make pie wedges, we apply a polar transformation to the shapes that were produced from the geometry
• Compute Aesthetics: aesthetic functions translate a graph into a graphic