They are lines on maps and planes in space, often extending beneath the ground and above it. No wonder so many disputes between individuals and countries arise along borders, the regions adjacent to boundaries. Many political boundaries find their origin in natural barriers such as coastlines, mountains, lakes, and rivers. But people cross these barriers with increasing ease and regularity. Roads, rails, and tunnels penetrate some of the most imposing mountain ranges.
Airplanes span the globe in a matter of hours, information in an instant.
And the barriers themselves can migrate. Natural barriers are transient, not eternal. Some boundaries follow lines of equal latitude or longitude. Examples include the straight or gently bowed lines which border many Canadian provinces and U.S. states on maps. Even the greatest familiarity with the land, however, is no guarantee that its resources have been identified.