<Table> <Tr> <Td> </Td> <Td> This article does not cite any sources . Please help improve this article by adding citations to reliable sources . Unsourced material may be challenged and removed . (December 2009) (Learn how and when to remove this template message) </Td> </Tr> </Table> <Tr> <Td> </Td> <Td> This article does not cite any sources . Please help improve this article by adding citations to reliable sources . Unsourced material may be challenged and removed . (December 2009) (Learn how and when to remove this template message) </Td> </Tr> <P> Because of its unique history, many of the boundaries of the political divisions of the United States were artificially constructed (rather than being permitted to evolve and drawn using natural features of the landscape). Therefore, many U.S. states have straight lines as boundaries, especially in the West . However, there are a number of states, particularly in the Midwest, North and South with at least partial river borders . </P> <P> Typically the boundary is the "thread of the channel", under a rule that the United States inherited from England, where it applies to boundaries between counties . There are at least four exceptions, where the boundary is one bank of the river rather than the thread of the channel: </P>

In which part of the u.s. is the majority of state boundaries based upon natural features