In the results of the plebiscite on the German-Danish border in 1920, Ubjerg had the highest proportion of German votes in the entire I. Zone. The reason that Ubjerg and the nearby towns of Tønder and Højer, despite their German voting majorities, remain in Danish territory today, is due to the fact that the vote in the I. Zone was held "en bloc": here only the overall result of the zone counted, whereas in the II. Zone the vote was held by parish. The dividing line between the zones was based on the so-called Clausen Line, which, according to the research of the Danish historian H.V. Clausen, approximately represented the "language and attitude boundary" between Germans and Danes, and as such roughly coincided with the dividing line between German and Danish church languages. In the west, however - and also at Ubjerg, where preaching was rendered exclusively in German - the Clausen Line was not oriented to the church language, but to a "natural border": the water system of the Vidå brook, which drains large parts of North Schleswig. Denmark wanted to avoid German influence here.