Evaluation of Coordinate Points Consistency in Medieval Geographical Manuscripts (the case of Ibn Sa'id's Data on the Southern and Eastern Mediterranean)

Abstract

The article develops a technique for analyzing mathematical data (longitude and latitude) characterizing the location of cities in medieval Arabic geographical manuscripts. The calculations made at the coordinates of 19 points given by the Arab-Spanish traveler of the 13th century Ibn Sa'id. These data are taken from his text and from the book of Abu-l-Fida referring to Ibn Sa'id. With the help of the Python - PostgreSQL technological stack for each pair of cities a set of spheroids was determined that fit for placement them in the corresponding coordinates. Then the options for intersecting the sets in all possible combinations are analyzed. The consistent exclusion of all possible combinations of cities from the entire set allows these cities to be arranged according to the degree of consistency of coordinates for any number of withdrawn points. The results tell us that most of the coordinates were not the result of astronomical observations. One of the tasks was to test a hypothesis that some of the cities the coordinates of which were determined more accurately served as “reference” points serving the basis for calculating coordinates of the rest of the cities. Complete consistency of coordinates was achieved with the exclusion of 14 cities from the set in the first version and 13 cities in the second one. However, the geography of the rest cities in Ibn Sa’id’s version does not support the “reference points” hypothesis. Abu-l-Fida’s version can boast a result that is more close to the hypothes, but to prove it one has to solve the problem of data origin used by Abu-l-Fida to correct coordinates. The technique described can be applied to any other set of coordinates of ancient geographical descriptions to evaluate the degree of their consistency and search for “reference” points.