8. Transformations

Mathematically, time is typically treated as being continuous. It can be divided as finely as we desire, and we usually consider each section of time as being of the same importance as any other section of the same length; we do not think of certain times as being intrinsically more important than others. For many purposes this concept of time – as a linear, continuous dimension – is all that is needed to visualize time effectively. This chapter deals with other purposes: when we want to distort time to give more importance to some regions, when we want to analyze time in terms of frequencies, and when we want to divide time into discrete chunks. The transformations suggested in this chapter should be used to modify the mappings between variables and coordinates, aesthetics and facetings, and since the transformations are often parameterized, those parameters can be put under interactive control to allow a range of transformations to be explored under user control. Transformation is an optional step in the pipeline between data and visualization, but it is a common need and can open up a broader set of possibilities for effective visualization of time data.