'P' is the key

[eggyk]

JSTOR: 

Parchment: 52.5 x 43.5 cm
Size of Map (velum): 26.5 x 25.5 cm

LOC: 

vellum (map):  22 x 19 cm
on sheet: 29 x 41 cm 

If you're saying Parchment=Sheet, where has the other 23.5cm height & 2.5cm width gone? That's almost half the height gone, and would be a huge reduction in overall size. I'm not implying this is the V.M. page- I am asking this as a straightforward question. If you can point to any work or documentary errors that might have caused that sort of reduction I would like to read that because that's a pretty significant trimming. 

The height went nowhere; you have quoted the measurements for a different document. The measurements are at the end of each section, so you -for some reason- have used the measurements directly before the relevant section (the pantect map).

   
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As already quoted here by oshfdk (thank you btw), the measurements in the JSTOR article are:

full size of parchment - 40 X 28 cm;
size of map (maximum extent measured) 19 X 26 cm.

Either way, I have -to the best of my ability- tried to align the paper in the same way as in your images. They don't actually match other than both having dark stains. his would apply to thousands of manuscript pages that have staining. 

   
       

If you think that I haven't aligned it correctly, please show a closeup of how specific features match.