I've been searching for a proper term to describe Ptolemy's odd translations of British place-names and wondering if they had come to the notice of other students of Ptolemy.

Gudmund Schütte, Scottish Geographical Magazine Vol 30 (1914) pp 57-77 Ptolemy's Atlas : A Study of the Sources 
http://www.mocavo.com/Scottish-Geographical-Magazine-1914-Volume-30/581485/85#77

and his expanded treatment

Ptolemy's Maps of Northern Europe, Copenhagen (1917)

wherein he describes "nostrification"

"The distortion prevailing in Ptolemy's barbarian names is in many cases of merely accidental nature. But in some cases we observe the working of a general factor, the tendency towards “amending” the unknown forms after better known models.
The tendency generally has a centripetal direction, resulting in a so-called “nostrification”. That is to say: the names from the far periphery are remodelled after those which occur within the Roman Empire, especially those from Italy or its neighbourhood." p 24 Maps of N Europe

and further on p 16 ibid

"The Greek constructor of the Ptolemaic atlas was not always successful in interpreting his Latin prototypes. His knowledge of Latin appears to have been rather inadequate."

In summary, Ptolemy is trying to make Barbarian place-names more familiar to his Greek audience. His, or his 'constructor's' poor Latin, and apparent willingness to translate non-Latin Barbarian place-names into Greek has had some unintended consequences. Scribal corruption often compounds the problem leaving us with some rather mysterious forms to deal with.

"Herculis" promontory Έρακλέους ἂκρον is one that most seem willing to accept as a name bestowed by sailors. PNRB 372: "Such places in Britain presumably had native names, not known to us in this case."

But, I think there is another answer.

DLG 164 *perkʷus 'oak' sub 'ercunia' with the recognized diminutive suffix -ula would give *Ercula 'little oak'. *Ercula or *Erculis would be just the sort of name for Ptolemy to nostrify.

Hartland Point (DEV) is the identification accepted by most, though PNRB 135 says "any of the headlands between Porlock and Braunton".

It so happens that these "little oaks" are a notable part of the landscape.
http://jncc.defra.gov.uk/protectedsites/sacselection/sac.asp?EUcode=UK0013047
Tintagel-Marsland-Clovelly Coast
"This site represents an extensive length of largely hard coastal cliff in south-west England, with a range of maritime influences and vegetation developed on hard neutral to acidic sedimentary rocks. It demonstrates a range of vertical or near-vertical cliffs with intervening slumped sections. The greater part of this very long site, totaling approximately 60 km, is west-facing, fully exposed to Atlantic storms and therefore strongly maritime in character. The section east of Hartland Point faces north and north-east and is relatively sheltered. 

This includes an unusual wind-pruned cliff woodland, the Dizzard...

Stretches of old sessile oak wood occur at various points along this section of coast. The trees are frequently wind-pruned, sometimes to the point where they are barely taller than the heather..."




Tom Ikins

The Roman Map of Britain
http://www.romanmap.com