Exactly, geographical features offer precise borders. Mountains are especially useful, as more often than not their economical value is small. Rivers are very different manner, they were very important part of nations infrastructure before railroads (and still significant afterwards, even today) and sharing river with your enemy is not perfect solution, but again it allowed to minimize disputes.

Mountains also offer protection from your enemies, which is always useful. This can be most clearly seen in WWI, but it was so since antiquity. Rivers also can serve as protective borders (look at European borders of Roman Empire), but significantly less so.