The phrase "a fair illustration" is correct and usable in written English.
It can be used when you want to describe an example or representation that is reasonable or just in its depiction of a concept or idea.
Example: "The chart provided is a fair illustration of the trends we have observed over the past year."
Alternatives: "a reasonable example" or "an accurate representation".
The goal could stand as a fair illustration of the Rangers' season so far.
Although this is a fair illustration of the way the indexes are generally employed, the underlying reasoning is defective.
The men gathered at No. 8 and the building they occupy offer a fair illustration of the broken lives and steadily growing hatred that characterize the Bosnian war.
An eighth le Carré feature film, Tomas Alfredson's "Tinker Tailor Soldier Spy," will be released on Dec. 9, and it's a fair illustration of the fiendish difficulties this sly, subtle storyteller's work presents to moviemakers.
The tenth clause of the conditions annexed to this bill of lading, and shown elsewhere, affords a fair illustration of the customary methods of connecting carriers to co-operate for their mutual benefit in carrying on transportation begun by one which must be continued by other lines over which the thing to be transported must go.
John William Strutt, 3rd Baron Rayleigh, depicted in a Vanity Fair illustration, December 1899.
By Vanity Fair; illustration by Risko.
The illustration shows a fair comparison between the presented approaches because the considered effective oversampling factor takes into account the bandwidth of the transmit signal.
There were placards: "All rape victims deserve a fair trial"; "Stop blaming rape victims" and one with an illustration of a police officer admonishing a top-hatted plutocrat and the slogan "Go to jail".
Defendants' variation on the visual joke of plaintiff's illustration does not, without an element of humor aimed at some aspect of the illustration itself, render it a parody and therefore a fair use of plaintiff's work.
But it seems a fair bet that Eric Gill would have relished coming up with the illustrations.
