The 'patat-friet border' or 'friet border' is the informal name for an idiomatic isogloss within the Dutch language area. To the north of this isogloss is mainly used the word fries, while to the south of it one says fries or fries.

The map is based on the results of a 1972 survey by dialectologist Jan Stroop, who wrote an article about it in 2005 that he illustrated with the map Patates Frites. The use of the words patat friet, petat, friet en frieten were then drawn in and the boundary between word use of chips and potatoes with a line, the "patatten-aardappel boundary".[1][2] The original map appeared in 1972, accompanying the article: ‘A fries with (..questions), in Communications of the Institute of Dialectology, Folklore and Nameskill.[3]