In German linguistics, the
Sankt Goar line,
Das-Dat line (that), or the
Was–Wat line (what) is an
isogloss separating the dialects to the north, which have a /t/ in the words
dat "that" and
wat "what", from the dialects to the south (including standard German), which have an /s/:
das, was. The line runs from east to west and crosses the river
Rhine at the town of
Sankt Goar.