Uerdingen line
The Uerdingen Line (German: Ürdinger Linie, Uerdinger Linie, Dutch: Uerdinger linie; named after Uerdingen by Georg Wenker) is the isogloss within West Germanic languages that separates dialects which preserve the -k sound in the first person singular pronoun word "ik" (north of the line) from dialects where the word-final -k has changed to word final -ch in the word "ich" (IPA [ç]) (south of the line). This sound shift is the one that progressed the furthest north among the consonant shifts which characterize High German and Middle German dialects.