NavList:

The Mappa Mundi in the Hereford Cathedral appears to be close in contruction to an azimuthal equidistant chart.  That is, the center of the chart is Jerusalem.  The direction to other locations from Jerusalem is shown.  Land masses are highly distorted.  I don’t believe that the Mappa Mundi used accurate distances from Jerusalem in its creation.  The Mappa Mundi is a religious chart and extends to only the known world for the time (1300 or so).  As such, it is fairly unreliable and not really useful for either navigation or astrology.  I really don’t think it will be useful to you.

 Mind you, I'm far from an expert in history.   Only two months ago, I thought Pliny was an unimpeachable source and revered anyone who quoted Pliny.   Now I'm a lot more circumspect.

From reading the article, I have the impression that these tables were mostly useful for astrology.   I don't know much about astrology either, so I got a "baby's first book" on astrology.    Evidently natal astrology is a big deal - the orientation of the stars and planets relative to your horizon, zenith, nadir etc at your birth time/date/location.   This required information about the longitude and latitude of where you were born.   So, for a practicing astrologer, it seems like a table of latitudes and longitudes of places where people might have been born (e.g. cities) would be a reasonable catalog under the circumstances.  

I tried finding some online maps from that period and there weren't a huge number available.   I recall there's a map in the Hereford Cathedral that has the Garden of Eden at the top and Jerusalem at the center - dating from the 14th century.     In plotting these points on my grid, I was impressed that I could find a reasonable outline of some areas.   There are some locations that seem to be in Turkmenestan that would be located in the Indian Ocean on the other hand.

Perhaps there are some Arabic maps from that period - although the one or two I saw were also lacking in detail.

John H.