For some further snippets of information, that may be of interest, see:
Glover, Michael, Wellington's Army in the Peninsula 1808-1814 (David and Charles, 1977).
Between pp. 163-66, Glover presents a "portion of the map of Portugal by William Faden, 1810".
This, presumably, is the same map referred to above by Nantiat.
And, as far as I am aware, the original map was published in early 1810 - perhaps in January.
In this version, both the route north described above via the south (or left) bank of the Mondego, and the route north from Castel (sic) Branco, are hi-lighted - converging at Celorico.
Unfortunately, Glover - although an excellent historian in many ways - does not provide a source for this version of the map.
So we do not know the answer to the questions: by whom, why or when the map was embellished in this way.
if i am ever fortunate enough to realise the opportunity of writing and publishing something on the third French invasion of Portugal, I would be strongly tempted to assert that this cartography and topographical knowledge underpinned Wellington's strategy, operations and logistics in the early stages of the campaign.