They render quantitative relations with a transparency that seems natural, so that, for instance, if we look at the changes in population across a series of years for a particular location, we can simply accept that from one year to the next rises or drops occurred in the numbers of persons alive in X city in X country at X time.
Think of the bar/line charts employed by Blevins that demonstrate the occurence of a cluster of words related to weather or gardening that are compared to months of the year along the x-axis