Q: What is the connection between “orthography” and “orthographic projection”? The definitions of the two terms seem unrelated.
A: We’ll have to look at their ancient Greek roots to see how “orthography” (the study of correct spelling) is related to “orthographic projection” (depicting three-dimensional objects in two dimensions, as on maps and in architectural drawings).
In ancient times, the combining forms ὀρθο- (ortho-) and -γραϕία (-graphia) had several different meanings that are now seen in the English words derived from them, according to the Oxford English Dictionary.
In Greek, ὀρθο- could mean straight, correct, or upright (that is, perpendicular). In “orthography,” the combining form “ortho-” means correct, while in “orthographic projection,” it means upright.
Similarly, -γραϕία could mean writing, drawing, or recording. In “orthography,” the combining form “-graphy” refers to writing, while in “orthographic projection,” its cousin “-graphic” refers to drawing. The Greek term comes from the verb γρᾰ́φω (graphō, write) and originally meant to scratch, as on a clay tablet.
The OED, an etymological dictionary based on historical evidence, defines “orthography” as “correct or proper spelling; spelling according to accepted usage or convention.” The dictionary’s earliest example is from a Middle English rendering of a Latin treatise on Roman warfare:
“Thi writer eek [also], pray him to taken hede / Of thi cadence and kepe Ortographie, / That neither he take of ner multiplye” (from Knyghthode and Bataile, 1458-60, by John Neele, a verse paraphrase of De Re Militari, circa 390, by Flavius Vegetius Renatus). In the citation, from the last stanza, future scribes are asked to preserve the rhythm and spelling in copying the work.
Although the adjective “orthographic” has been used since the early 1800s in reference to “orthography,” it originally appeared in the sense you’re asking about, “of a projection used in maps, elevations, etc.,” according to the OED.
The dictionary’s first example is from a review of a 17th-century book that discusses the optical projections from an astrolabe, a device once used to make measurements in astronomy:
“The Orthographick Projection, by Perpendiculars falling from the respective Points of the Circles of the Spheare, on the Projecting Plain: Such a Projection, if the Plain be the Meridian, Ptolemy called the Analemma” (from Philosophical Transactions of the Royal Society, London, 1668-69).