Thursday, November 10, 2022

The Commentary on Pleiades

 The Mycenaean Atlas Project is more than just a Bronze Age gazetteer.  It is an accessible viewer for the entire ancient world - and at every period. It accomplishes this goal by integrating several very different data sets.  Here's an example:


The city of Aigion in Achaea as displayed in the Digital Atlas

One of those data sets is Pleiades.  But how do you handle or display a dataset with as many serious defects as Pleiades?  Its deficiencies are of three kinds.  Of Pleiades' approximately 39,000 records about 7,000 have no lat/lon coordinates at all.   As a result, these points cannot be displayed at all and  why they are in the dataset in the first place is a mystery.

Pleiades next problem is the 5,000 or so sites for which the lat/lon pairs are rounded to the nearest quarter degree.  This indefensible practice (and never corrected during the entire 20-year existence of this DB) puts these sites off by about 12 km. on average.  Even worse, it creates about 400 or so 'stacks' in each of which some 10 to 20 sites have exactly the same rounded coordinates and cannot be disambiguated.  (See the example of Boreion, below.)

The remainder 26,000 sites are simply inaccurate.  They are off by about 900 m. on average because this part of the DB was intended for the Barrington Atlas - a printed product in which accuracy, at the given scales, could never be better than a km. or so.  Accuracy is expensive and you never pay for more than you need.  This practice was fine for a printed product but a disaster when moved to the digital world in which representable locations are accurate to less than a meter.  The need to develop precise and accurate data for the digital world is far more urgent than it is for the world of the printed atlas.

When showing Pleiades data in a gazetteer viewer such as the Mycenaean Atlas Project the overwhelming temptation is to correct these numerous errors by adding additional information to the Pleiades data. Providing accurate lat/lon pairs is a chief priority.  The design problem is, somehow, to add that information in a way that new versions of the Pleiades database don't write over what people external to Pleiades, such as myself, have added.  How do we best add and store supplemental and updated information for Pleiades sites and how should this new data be displayed?

What is required is a Commentary on Pleiades.

      To support this Commentary I created a new DB table that would hold any additional information or corrected lat/lon pairs.  A table that is independent of the Pleiades database would not be overwritten by new versions of the Pleiades database.  It would exist alongside the Pleiades DB. And yet the new data in this table could still be connected to the old Pleiades database through the Pleiades id no.  That way if there was an entry in the new table for any specific Pleiades site record my browser would display THAT corrected/additional data instead of the incorrect Pleiades data.  This required that I accompany my new DB table with a new browser page in .html.  This will be the new Commentary on Pleiades page which stands between my viewer and Pleiades itself.  In addition to corrected information this new page maps the Pleiades places to their correct location on a new map instead of to the incorrect rounded quarter-degree locations where they are now displayed.


Design of old and new interaction with Pleiades.


The upper half of this diagram shows the current situation; the Mycenaean Atlas Project takes information from the unmodified local copy of the Pleiades database and displays it.  That display has a button that, when clicked, takes the user back to the original Pleiades page for more information.

The lower half of the diagram shows the new design.  In addition to the local copy of the Pleiades database as before (orange), there is a brand-new table that contains my own contributed material.  On the browser map, when the user clicks the Pleiades icon for more info they don't go to the Pleiades page as before but to the new Pleiades Commentary page that shows the corrected lat/lon pair along with more info and a browser map that shows the icon in its corrected position.  A link on that supplemental commentary page will send the user to the original Pleiades page (dashed line).

This whole process is transparent to the user who will only see the new commentary page when he or she clicks on a Pleiades place for which I have created commentary. 

The new Pleiades Commentary page will look like this (annotations in red):


The new Commentary on Pleiades page (here for Belminatis, Pleiades 570152).


Now I'd like to show a situation in which this commentary is invaluable.

Mt. Boreion in Arcadia is Pleiades 570158.  Pleiades gives its position rounded to the nearest quarter degree like this: 37.25, 22.25.  This is exactly the same position as seventeen other Pleiades sites.  I list them here:

Pleiades grouping 18 sites at the very same location: 37.25 N, 22.25 E.

This sort of practice is common in Pleiades and it must be corrected.  Even a casual user does not deserve to have all these sites shown in the identical location.

I corrected the rounded position of Boreion (37.25 N, 22.25 E) to  37.429300°,  22.342900°.  On the next map I compare my position, Topostext's position, and  Pleiades position:

Placement of Mount Boreion (Attica) in Pleiades, Topostext, and Mycenaean Atlas Project.


I have not adopted Topostext's position here but the rounded Pleiades position (at the bottom of the map) is 21 km. from my proposed location and almost 19 km. distant from Topostext's. 

My Commentary to Pleiades will change all this. If you search for 570158 or 'Boreion' and display it on the digital atlas you will be shown this next page (Be sure to select 'Pleiades' layer from the (not shown) map layer selector on the top right):

Mt. Boreion (Pleiades 570158) displayed in correct position.



The top link in the info box ("Pleiades (S) 570158") will not bring the user to the main Pleiades page for 'Boreion'.  Instead the new Pleiades Commentary screen will be displayed:


Commentary on Pleiades - supplemental information page


My goal for the future is to correct all the locations whose lat/lon coordinates have been rounded.  For the Peloponnese alone this amounts to about 160 such rounded markers.  Presently there are about 150 corrected Pleiades sites (primarily for the Peloponnese) and the work of adding corrections to Pleiades will be ongoing.












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