Where is Thule?

Researchers equal world map of Klaudios Ptolemy

Klaudios Ptolemy's copyright expired
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Where is the almost mythical island in the far north, which the ancient Greeks already called "Thule" around 325 years before the turn of the century? Scientists from the Institute of Geodesy and Geoinformation Technology of the Technical University of Berlin (TUB) try to solve the mystery by straightening out the famous world map of Klaudios Ptolemy.

The Greek geographer had already designed the world map in the second century after the turn of the century. Thule also thinks of this: six days' travel north of Britain, this island is to be found according to earlier data, so Ptolemy.

Error about errors

Exactly with such data but the problem lies. Although Ptolemy has listed more than 6, 000 places between China, Sri Lanka, Central Africa, and Britain in his maps and books, the geographic data is not always right for a variety of reasons. For example, when copying these works, mistakes have repeatedly crept in, making it difficult to interpret the map. However, many places no longer exist or their name has changed so much over the centuries that it can hardly be recognized.

World Map of Klaudios Ptolemy © J. van Loon, copyright expired

On top of that, the original information in the world map of Ptolemy was not always completely correct. Thus, the Greek geographer often relied on the testimony of other researchers who sometimes lived centuries before him. Even then, however, there were certainly mistakes in the tradition. On top of that, the distances at that time were still measured in stages, which were not always uniformly long.

So if you want to use the map of Ptolemy in the 21st century, for example to find Thule or other historical places, you first have to uncover all these mistakes. For this it is necessary to equalize the map until it corresponds to a modern map with its relatively exact geometrical information. This is precisely the task TUB researchers Eberhard Knobloch, Dieter Lelgemann and Frank Neitzel have tackled in a new project. display

From "Toletum" to "Barcino"

First of all, they need the help of the ancient scholar Andreas Kleineberg. He has from the more than six thousand statements of Ptolemy to identify modern places. For some cities like Toledo or Barcelona this works quite well, because they still exist today and their old names "Toletum" and "Barcino" are still known. But many other places have long disappeared from modern maps or no one knows where they might be. As good as possible, Kleineberg now tries to find the modern designations through references. Depending on the state of things, he also labels his results as "safe, " "likely, " or "uncertain."

The geodesists then compare the historical values ​​for geographical lengths and latitudes with the modern values. In doing so, they discover so-called gross and systematic errors: the former have accumulated during the copying of the manuscripts, whereas the latter arose when exact regional maps were not correctly combined to form an overall map. As a result, the different parts of the map are displayed in different size ratios and also shifted against each other.

Geodetic deformation analysis

By means of the "geodetic deformation analysis" Neitzel and his colleagues try to divide the world map into individual areas with uniform changes or deformations. Specially developed computer programs then transfer the historical values ​​of the respective map parts with as uniform as possible deformations into modern latitude and longitude grades. It has already been shown that the map of Ptolemy is distorted on a scale of 2 to 3 or 5 to 7. Lelgemann has also solved the mystery of Thule with this work: It is the island Smola in front of the old king town Trondheim in Norway.

(idw - Technische Università t Berlin, 21.08.2007 - DLO)