Circa 1698 a mysterious stranger, known only by the pseudonym B.E. Gent., published a book by the title of A New Dictionary of the Terms Ancient and Modern of the Canting Crew. This work was the first dictionary of English slang, and as such set the tone for many such works in the years to come.
One of the odder choices that B.E. made was to refer to vagabonds as 'the Canting Crew'... and then number them. At the time this was considered good fun, and for the next century or so this tradition continued.
Rufflers, c. the first Rank of Canters; also notorious Rogues.
Upright-men, c. the second Rank of the Canting Tribes, having sole right to the first night's Lodging with the Dells. (Dells are elsewhere defined as "young bucksome Wenches")
Hookers, c. the third Rank of Canters. (At this time, hookers referred to pickpockets.)
and so on to...
Kinchin-morts, c. the Twenty seventh and last Order of the Canting Crew, being Girls of a Year or two old, whom the Morts (their Mothers) carry at their Backs in Slates (Sheets) and if they have no Children of their own, they borrow or Steal them from others.
Note that these are not ranked in any particular order; rank the fifth consists of children raised to be pickpockets and cat burglars (wild-rogues), the sixth are horse thieves (priggers or prancers), seventh are beggars (palliards) and ninth are thieves (priggs). They are not ordered alphabetically, meaning that they are listed out-of-order, interspersed randomly throughout the dictionary. While B.E. spent some time ranting about the evils of "Gypsies, Beggers, Thieves, Cheats", he did not bother to say a word on the development of his taxonomy.
However, we must assume that this was rather clever in its day, because later dictionaries of slang copied them down. I believe that this tradition largely died out after Francis Grose's famous 1811 Dictionary of the Vulgar Tongue, which kept the rankings but updated the definitions for modern readers. However, the Dictionary of the Vulgar Tongue is still fairly common today (including on E2), so one still finds mysterious references to "the order of the canting crew" with no explanation given or hinted at.
The full text of A New Dictionary of the Terms Ancient and Modern of the Canting Crew can be found here.
A kind denizen of the World Wide Web has ordered the Canting Crew by rank in one easy reference guide: We-are-rogue's list can be found here.