@spendius,
And if you ever get a chance to study the globe we call earth, you'll see names for almost all of it. Maps has to be revised, because there's a huge difference between geographical (the physical) and political boundaries. During the past century, political boundaries have changed frequently even though the geographical has changed very little. A little knowledge of your back yard would do wonders for your geographical and political understanding of this planet.
Geographical are natural borders. Some geographical features that often constitute natural borders are:
Oceans: oceans create very costly natural borders. Very few nation states span more than one continent. Only very large and resource-rich states are able to sustain the costs of governance across oceans for longer periods of time.
Rivers: some political borders have been formalized along natural borders formed by rivers. Some examples are; the Rio Grande border (Mexico-USA), the Rhine border (France-Germany), and the Mekong border (Thailand-Laos)
Lakes: larger lakes create natural borders. One example is the natural border created by Lake Tanganyika (Congo-Burundi-Tanzania-Zambia)
Forests: denser jungles or forests can create strong natural borders. One example of a natural forest border is the Amazon rain forest (Colombia-Venezuela-Guyana-Brazil-Bolivia-Peru)
Mountain ranges: