# Carpet Plot - Temporal Raster Plots

Temporal Raster Plots

Another visualization that is sometimes called a carpet plot is a graphic representation of occurrences in a certain temporal relation. Each occurrence is registered in a Cartesian coordinate system, in which both axes show time, have different time resolutions: one axis shows slices of data, the other some sensible interval. A common example would be that one axis shows hours in a day, the other days in a year.

In a 2D plot, the value to be plotted is coded with an intensity or a color. In the 3D variant of the plot, it is often coded as a height. When visualized, particularly the color-coded variant of the plot may easily show a carpet-like pattern.

Carpet plots make it easy to show time-based relations within a large sets of time-interval data and often make it easy to recognize local maxima and minima. Assuming the chosen time division is related to the events, it is also easy to recognize global and local patterns, such as recurrent events.

In the following example, the data is one year's worth of measurements of the outdoor temperatures in Augsburg, with four samples taken per hour. In the according carpet diagram, each column represents a day in the year and contains the values for that day (from 0:00 until 23:45). Despite the high number of measure points (about 35000) it is easy to disdistinguish local and global patterns.

Note the similarity to beat graphs as described by Werner Van Belle.

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Whoever plots the sin, thou point’st the season;
‘Tis thou that spurn’st at right, at law, at reason;
And in thy shady cell, where none may spy him,
Sits Sin to seize the souls that wander by him.
William Shakespeare (1564–1616)

What’s this, Aurora Leigh,
You write so of the poets and not laugh?
Those virtuous liars, dreamers after dark,
Exaggerators of the sun and moon,
And soothsayers in a tea-cup? I write so
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Elizabeth Barrett Browning (1806–1861)