Time as a Coordinate
This chapter deals with the most common method of presenting time in a plot of data – using it as a coordinate to locate elements of the graphic. The time plot, with time on the horizontal dimension and a continuous value plotted as a moving line on the vertical axis, epitomizes the power of this principle. Most books on time series analysis will lead off with time series displays, inviting the reader to observe them and then using the plots to motivate the following analysis. In this chapter we will start at a more basic level – the 1-D chart with time as a single dimension. Variants and decorations for this very simple chart will be discussed; aesthetics that map other variables play a key role, as do positional modifiers that stack elements and the use of additional elements to indicate patterns. Sometimes a second dimension will be used, straying into the territory of the next chapter, but the thrust of this chapter is to explore how time can be mapped to a single coordinate so as to show patterns and enable action.