Saturday, February 18, 2017

The Depiction of Time and Space out of Scipio's Dream

It is common to think of statistical graphics and data visualization as relatively modern developments in statistics. In fact, the graphic representation of quantitative information has deep roots, reaching into the histories of the earliest map making and visual depiction of astronomy, and later into thematic cartography and many other fields. The idea of coordinates was used by ancient Egyptian surveyors in laying out towns, earthly and heavenly positions were located by something akin to latitude and longitude by at least 200 B.C., and the map projection of a spherical Earth into latitude and longitude by Claudius Ptolemy (85–165) in Alexandria would serve as reference standards until the 14th century. 

Planetary movements shown as cyclic inclinations over time, by an unknown astronomer, appearing in a
10th-century appendix to commentaries by Macrobius on Cicero’s Somnium Sciponis. This is the earliest
known 2-dimensional charts (plotting time vs. celestial latitude; an apparent anomaly is that it appears to
show the celestial latitude of the Sun varying with time); the scribe used horizontal and vertical lines as
aids, resulting in a picture strikingly similar to modern graph paper as it did not become commonly used
before the mid 19th century, some 700 years later. This picture is a notable anomaly, as the earliest
comparable "graph" diagram do not emerge prior to the late medieval period, some 250 years after
this drawing was made. Source: Wikimedia.

Among the earliest graphical depictions of quantitative information is the above anonymous 10th-century multiple time-series graph of the changing position of the seven most prominent heavenly bodies over space and time. The vertical axis represents the inclination of the planetary orbits; the horizontal axis shows time, divided into 30 intervals. The sinusoidal variation with different periods is notable, as is the use of a grid,suggesting both an implicit notion of a coordinate system and something akin to graph paper, ideas that would not be fully developed until the 1600-1700s. In the 14th century, the idea of plotting a theoretical function (as a proto bar graph) and the logical relation between tabulating values and plotting them appeared in a work by Nicole Oresme (1323-1382), Bishop of Liseus, followed somewhat later by the idea of a theoretical graph of distance vs. speed by Nicolas of Cusa.