In the north and northwest, the Swiss Plateau is sharply delimited geographically and geologically by the Jura Mountains. In the south, there is no clear border with the Alps. Usually, the rising of the terrain to altitudes above 1500 metres AMSL (lime Alps, partly sub-alpine molasse), which is very abrupt in certain places, is taken as a criterion for delimitation. Occasionally the regions of the higher Swiss Plateau, especially the hills of the canton of Fribourg, the Napf region, the Töss region, the (lower) Toggenburg, and parts of the Appenzell region are considered to form the Swiss Alpine foreland in a narrow sense. However, if a division into the three main regions Jura Mountains, Swiss Plateau and Alps is considered, the Alpine foreland belongs clearly to the Swiss Plateau. In the southwest, the Swiss Plateau is confined by Lake Geneva, in the northeast, by Lake Constance and the Rhine.
Geologically, the Swiss Plateau is part of a larger basin that extends beyond the border of Switzerland. At its southwestern end, in France, the plateau, in the Genevois, ends at Chambéry where Jura and Alps meet. At the other side of the Lake Constance, the plateau continues in the German and Austrian Pre-Alps.
Within Switzerland, the Swiss Plateau has a length of about 300 km, and its width increases from the west to the east: In the Geneva region, it is about 30 km, at Bern about 50 km and in eastern Switzerland about 70 km.
Many cantons of Switzerland include a part in the Swiss Plateau. Entirely situated within the Swiss Plateau are the cantons of Zurich, Thurgau and Geneva; mostly situated within the Swiss Plateau are the cantons of Lucerne, Aargau, Solothurn, Bern, Fribourg and Vaud; small portions of the Swiss Plateau are situated in the cantons of Neuchâtel, Zug, Schwyz, St. Gallen and Schaffhausen.
The geological layers of the Swiss Plateau are relatively well known. The base level is crystalline basement which outcrops in the central crystalline Alps as well as in the Black Forest and the Vosges mountain range but forms a deep geosyncline in the Swiss Plateau and in the Jura (see also Jurassic). Around 2500 – 3000 metres below the surface, but considerably deeper near the Alps, the drillings have hit the crystalline basement. It is covered by unfolded strata of Mesozoic sediments, which are part of the Helvetic nappes. Its depth gradually decreases from about 2.5 km in the west to 0.8 km in the east. These layers, like the ones of the Jura Mountains, were deposited in a relatively shallow sea, the Tethys Ocean. Above the Mesozoic layers, is the Molasse, consisting of conglomerate, sandstone, marl and shale. The uppermost layer consists of gravel and glacial sediments that have been transported by the glaciers of the ice ages.