geographic regions: the Swiss Alps, the Central Plateau and the Jura, each corresponding to very different geological realities. In addition, two small regions are not part of those three. The first, north of the Rhine in the Basel area, is situated beyond the Jura. The second, on the south in the Mendrisio area, is located in the Po Valley. But these two territories are not extensive in comparison to the total area of the country. The Swiss Alps occupy the southern part of Switzerland. They were formed by the thrust of the African plate, which also caused the formation of the Jura in the north-east and the plateau between the two massifs. In terms of area the Alps constitute about 60% of the country, the plateau 30% and the Jura 10%. The rugged terrain of the Jura and the Alps are very sparsely populated, except for some large valleys such as the Valais. Most of the population lives on the plateau where the country's major cities such as Geneva, Zurich, Basel, Lucern, and Bern are located. Central Plateau The Swiss Plateau extends from Lake Geneva on the French border across central Switzerland to Lake Constance on the German and Austrian borders. 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, which is very abrupt in certain places, is taken as a criterion for delimitation. The plateau has an average altitude of . Even though the Swiss Plateau forms a basin, it is by no means a flat territory and it is covered with rolling hills, lakes and rivers. Most of Switzerland's large lakes are located in the plateau. Both Lake Geneva () and Lake Constance () are located in the plateau but are shared with other countries. The largest lake totally in Switzerland, Lake Neuchâtel (), is located in the Swiss Plateau. The Swiss Plateau is crossed by three great river valleys (Rhône, Rhine and Aare) and the smaller Thur valley. While the headwaters of these four rivers all lie in the Alps, they all cut across the plateau between the Alps and the Jura mountains. Near Schaffhausen the Rhine passes through the Rhine Falls, Europe's largest waterfall. The Rhine Falls are wide and . The plateau occupies about