The term "boundary" most commonly refers to an imaginary line separating one country from another. There are also boundaries between smaller political units, such as states, provinces, and counties. Political boundaries are always human devices for partitioning areas, but they often follow physical features, such as rivers or mountains. For a part of its length, the boundary between the United States and Mexico follows the Rio Grande. The boundary between France and Spain follows the crest of the Pyrenees. The area on either side of a boundary is known as a border or, in some cases, a frontier.

Geographers are concerned with other kinds of boundaries as well. For example, there are linguistic boundaries between areas where different languages are spoken, economic boundaries between different marketing centers, and social boundaries between different neighborhoods. Usually these kinds of boundaries are not sharply defined the way the political ones are; rather, they represent transition zones.

This information is an excerpt from our geography encyclopedia, Exploring Your World: The Adventure of Geography.

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