The first thing that struck me was how computerish the lines looked.
It's my scanner.
The first thing that struck me was how computerish the lines looked. When I checked the link you included, I wondered if you simply traced the digital version.This would somewhat contradict the idea of redoing it in pen. Do you have a sample or a reference of how the original Ptolemy rendition of Britain looked? If you take the trouble of doing it in pen, I think you should try to replicate a looser rendition or even your own interpretation of a hand-drawn coastline rather than follow a vectorized version.
The original maps are lost in time so all the maps out there are based on the coordinates from the book. This is the reason my version looks like the same as the one at the Web. For the final version I'll use more colors (red for the cities, blue band for the coastline and some green on the inland?) and more loose line and maybe some reference from satellite photos for the islands.