Newig, J.. Die Küstengestalt Nordfrieslands im Mittelalter nach historischen Quellen. In: Schernewski, G., Dolch, T. (eds.). Geographie der Meere und Küsten. Coastline Reports (1), pp. 23-36. 2004.

There is made an attempt to reconstruct the medieval coastal line i. e. coastal situation of Northern Frisia according to historical sources. A very important basis for that is the “Earth Book” of the Danish King Waldemar the Great, who - after the loss of his entire silver supplies - had a complete list of the local sources of income made. So lots of historical sites were mentioned for the first time ever. Of great importance is a list of islands in Waldemar’s Earth Book, which tells us which parts of the coast were seen as islands at the time of about 1230. The evaluation of this actually well-known source was made rather difficult by the fact that there are mentioned three islands whose assignment had not been possible so far. By comparing them with another list of small administrative units that is mentioned in the same source the names of the islands are assigned to such ancient islands that can still be identified as land masses today. Since islands at the tidal coast of the North Sea are always separated from each other by natural tidal channels it is possible to reconstruct also the ancient ones. A second source is the reconstruction of the old church organization into “Probsteien”, (praepositurae) which were taken from old episcopal registers and destribed cartographically by W. Jessen in 1904. It is particularly interesting to project these results onto a map of the medieval cartographer Johannes Mejer, who in his New Description of the duchies of Schleswig and Holstein - published in 1652 - tried to reconstruct the situtation at the time of about 1240, a map that has so far been evaluated as rather inexact and therefore relatively worthless by a number of historians, but on the whole as true by hydraulic engineering specialists. Finally a hypothesis is undertaken that the three “praepositurae” are the three saxonian Islands of Ptolemäus (ca. 150 A.D.).