Why do many states in America have straight borders?

  • Most of the states in America have straight borders. Many appear to have been designed to be free from any curves or angles. Why were they designed like that?

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    "How the States Got Their Shapes" is a relevant series if you're interested in such things.

  • user1530

    user1530 Correct answer

    4 years ago

    The western united states came into being long after the eastern (states were added from east-to-west). As such, a bit more time/thought was put into getting them set up with their borders.

    In general, there's two types of borders:

    • natural
    • man-made/defined

    When the border is natural, such as a river, that's the easiest solution, as the river, though windy, is a pretty clear separation of land mass.

    When we have to make the borders ourselves, the easiest line to create is a straight one. As such, whenever possible, straight lines were used.

    In other words, the answer is: geometry

    For a much more detailed history of each state's borders, the History Channel created a series about this very topic:


    Rivers do have one complication; they tend to move their course over time, which either shifts the border, or creates land on the "wrong" side.

    @origimbo yep. That definitely happens, though less of an issue in the age of GPS and GIS.

    @blip: Why would GPS make it less of a problem? All it does is tell you that the river has moved. If the river is defined as the boundary, you still have a problem. And if you define the boundary as where the river used to be, you have a different problem :-)

    @jamesqf AFAIK, natural boundaries today have all been replaced with specific boundaries...typically the center of the body of water at the time of defining. That can remain immovable even if the river moves. That can lead to, of course, 'island' of states surrounded by water. I believe this has happened in a few states.

    Of course, conversely, the 'simple straight' borders has also caused issues in the past...such as this isolated part of WA state: https://en.wikipedia.org/wiki/Point_Roberts,_Washington

    Parts of Kentucky got put on the Indiana side of the Ohio river because of earthquakes.

    See Border irregularities of the United States for others. If you look north of Memphis, TN on a map, it seems like the Mississippi has shifted a bit, making the old borders a bit strange.

    @origimbo - It sounds good, but in practice the law is pretty foreward here: when the river changes the border doesn't. See for example this case.

    "man-made" essentially answers the question.

    @indigochild That depends who's law. International law tends to stick in the middle of navigable rivers, so that both countries maintain access.

    There must be more types of borders. In Europe for instance, I can't think of any border that forms a straight line on a large scale, but not all borders follow natural courses like rivers. Some are just grown historically, I guess.

    There are lots of borders in Europe that don't follow a natural feature but are still not straight. Many follow mountains, but the exact path is still quite arbitrary. Generally, straight lines indicates that the borders were drawn up "from above" on a map, rather than codifying existing reality on the ground.

    @indigochild That's oversimplifying almost to the point of being wrong. When the river changes *suddenly* the border stays where it was. When the river changes *gradually* (e.g. by erosion) the border moves with it. -- This is covered in the very first paragraph of your link.

    @MatthewLeingang Floods, not earthquakes.

    @phoog thanks. No wonder I couldn't find a link to back up what I learned as a kid.

    @TorKlingberg And many of the European borders ultimately come from war and conquest, sometimes with discussion in peace settlements afterwards. Some of these more or less reflect the position of the front line when one side surrendered.

    Using rivers as borders in poorly-surveyed areas can lead to problems too. The Treaty of Paris (1783) assumed that the Mississippi River went much further north than it actually did, and the border had to be renegotiated 35 years later once better surveying was done. See the Wikipedia article on the Northwest Angle for more details.

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Content dated before 7/24/2021 11:53 AM

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