These prints are an exercise, using a method of theirs to display information in relation to averages. Originally used for displaying hours of sunlight the technique is here used to display density in traffic flow. Information is collected via automatic counters at one point on a national road, and an average is calculated every 15 minutes. If a given day is above average it will be present as black and if below will simply be absent.

Table reads as follows:

Left to right, each block representing 15 minutes.
Bottom to top, each block representing the given day of the week.

The original sunlight profiles of Monkhouse and Wilkenson:

As noted by Edgar Tufte:

The image is inverted to extend the metaphor of light expanding into dark