Geography Reference
In-Depth Information
Natural boundaries are based on some aspect of
physiography
— physical landforms. While
diverse aspects of landscape may be called upon, three are particularly common. The United
States provides abundant examples of each type (see Figure 14-3):
Figure 14-3:
Examples of nat-
ural and geomet-
ric boundaries in
the
United
States.
Shorelines:
TheAtlanticCoastboundaryofFloridaandthemaritimebordersofAlaskaare
good examples. The shorelines of the Great Lakes States are relevant to some extent, though
the border with Canada runs through the lakes rather than following the shoreline.
Rivers:
The New Jersey-Pennsylvania border (Delaware River); the Illinois-Iowa border
(Mississippi River); and the Oregon-Washington Border (Columbia River). Quite typically,
the border is not the left bank or the right bank, but instead an imaginary line that runs down
the middle of the waterway.
Ridgelines:
The crest of a ridgeline in the Bitterroot Mountains marks the border between
Idaho and Montana. Similar crests in the Appalachian Mountains mark the boundaries
between Virginia and West Virginia, and between North Carolina and Tennessee.
The principal advantage of natural borders is that they are based on things that can be readily seen,
agreed upon, and mapped. In contrast to an occasionally questionable ethnic boundary, there should
be no question as regards to the location of a river, coast, or ridge. They are not necessarily perman-
ent, however. As you can see in Chapters 6 and 7, powerful tectonic and gradational forces build up
and wear down Earth's surface over time. Rivers in particular may change course as a result of a ma-
jor flood or cataclysmic event. But the advantages of natural boundaries are powerful. As a result,
many boundaries are based on this feature.
Geometric boundaries
