The fall line is a line on a
map, usually approximately
parallel to the
coastline, which is drawn between the
waterfalls or
shoals which first block navigation from the
ocean up the
rivers. On one side of the fall line is a coastal
plain; on the other is hilly or mountainous country.
Settlements often are established right around the fall line so that items being shipped upriver can be unloaded there, since it's as far as they can go by that route. For example, a map of the fall line in the U.S. South nearly connects Baltimore, Maryland; Washington, DC; Richmond, Virginia; Raleigh, North Carolina; Columbia, South Carolina; Augusta and Macon, Georgia; and Tuscaloosa, Alabama.