Speyer line
In German linguistics, the Speyer line, or Main line is an isogloss separating the dialects to the north, which have a geminated stop in words like Appel "apple", from the dialects to the south, which have an affricate: Apfel. The line begins in Alsace near Strasbourg, and runs north-east to Thüringen, crossing the Rhine at Speyer. After passing close to Erfurt, it turns south-east and continues into the formerly German-speaking parts of Bohemia. It can be observed well by the fact that place-names containing an uncombined /p/ phoneme mostly lie to the north of the line, while those with an affricate /pf/ mostly lie to the south.
