What was the river Ister in the time of Strabo? A mathematical approach

In this paper, we introduce a novel method for map registration and apply it to transformation of the river Ister from Strabo's map of the World to the current map in the World Geodetic System. This transformation leads to the surprising but convincing result that Strabo's river Ister best coincides with the nowadays Tauernbach-Isel-Drava-Danube course and not with the Danube river what is commonly assumed. Such a result is supported by carefully designed mathematical measurements and it resolves all related controversies otherwise appearing in understanding and translation of Strabo's original text. Based on this result we also show that {\it Strabo's Suevi in the Hercynian Forest} corresponds to the Slavic people in the Carpathian-Alpine basin and thus that the compact Slavic settlement was there already at the beginning of the first millennium AD.