It lies in the extreme northeast corner of the canton and includes the districts of
Aarwangen and
Wangen, and part of the district of
Trachselwald. It is surrounded by the cantons of
Solothurn,
Aargau, and
Lucerne. It is connected to the rest of the canton of Bern only in the south, where it borders on the Emmenthal. The Oberaargau lies on the
Swiss Plateau between the large population centers of
Bern and
Zürich and has therefore become a major thoroughfare for traffic running both east and west and north and south. The Aar River traverses it from west to east, and the primary motorway of Switzerland (the A1) and the main Bern-Zürich railway run through it, making it a central transport region. The primary city is
Langenthal, and the towns of
Herzogenbuchsee,
Wangen, and
Aarwangen are important transportation centers. Since the building of the motorway, the primary economic development has taken place in the north, at the foot of the
Jura Mountains, particularly in the towns of
Wiedlisbach and
Niederbipp. The highest point in the Oberaargaus is the
Höllchöpfli in the municipality of
Rumisberg, at 1231 meters, and the lowest point is on the Aare at
Wynau, at 405 meters. ==Administrative district==