Why are the USA and Canada's states border so straight?

CGP Grey has a video about this nice border between Canada and the USA, and how it isn't that straight as you think.

https://youtu.be/qMkYlIA7mgw

edit: In this video Grey explains why the border between Canada and the US is supposed to be straight, why it isn't and some rather odd analogies.

The shape of borders reflects the history and commerce at the time. In the eastern US, borders are often formed by geographic features because transportation at the time was very relevant - and transportation largely depended on waterways. For instance, the northern border of Indiana is straight - but it's about 10 miles further north than it would be as an extension of the Ohio border. This was made to give Indiana access to Lake Michigan.

The western border of Massachusetts is straight except for the southernmost few miles. This happened because of a mountain range. This little notch would have been almost impossible to police from MA, but is easy to reach from New York.

Going further west, there are several factors that led to straighter borders.

• As others pointed out, less white population.

• Less was even known about the geography of those regions, especially pre-Lewis&Clark. A few of the borders are quite old. For example, the northern border of Tennessee/Kentucky/Arkansas/Oklahoma/New Mexico/Arizona - it was shifted north a little starting in Oklahoma. Another example are the borders between New York and Pennsylvania, and between PA and Maryland/West Virginia. Those borders were originally intended to extend all the way through the Continent.

• Much of the Midwest has far fewer natural features that would lend themselves as border. There's the Mississippi river, of course, but not much going west from there until you get to the Rockies.

• When those borders were set, transportation depended on railroads more than rivers. Access to navigable waterways was far less important than in areas settled earlier.

• A lot of the economy in the western US depended on resources such as gold, silver, later also oil etc. These resources generally don't have perfectly known boundaries. Straight lines would come about either to protect the resource and a buffer around it, or conversely, when a several groups claimed the same resource, and it had to be split.

• Some boundaries in the West still are determined by rivers, for instance the Colorado between Arizona/Nevada and California, or the Columbia between Washington and Oregon.

• I believe the border of Wyoming had something to do with Yellowstone, although I don't recall the exact connection.

The only place you really have the large straight-line International border is West of the Great Lakes (up until Vancouver)¹. Probably the most succinct reason it was made that way, rather than at natural boundaries like everywhere else, was that neither side actually had any citizens settled in that area yet.

Originally (post-Louisiana Purchase), the USA claimed the entire Mississippi(/Missouri) watershed, while Britain claimed the Hudson Bay watershed. However defining an exact watershed was no simple matter, particularly when native nations controlled most of the headwater areas.

So after the War of 1812, the USA and the British agreed to simplify the border on the west side of the Great Lakes at the 49th parallel. Again, native nations still controlled most of this area. The borders to the East where both sides had cities remained at more natural boundaries.

For the US states, generally borders tended to get set up while the areas were still territories (mostly uninhabited by American Citizens), so cultural communication/travel barriers weren't as much of a consideration. Additionally, there was a feeling in the US Congress that all new US states should be roughly the same size, which led to a lot of territories having relatively arbitrary lines drawn through them to make properly-sized states. Slavery also ended up having a hand in a surprising number of state border placements (for example, its almost solely responsible for Oklahoma's weird "pot" shape, made up of mostly straight lines.)

If you are generally interested in US borders, a good book to pick up is How the States Got Their Shapes. There was also a series by that name produced for The History Channel. You might be able to find some of it from your favorite streaming TV sources.

Canada I don't know as much about, but its pretty clear that their even sparser population led to them not caring as much about keeping the physical size of their provinces down.

^{1 - Yes, there's a tiny straight bit on the northern border of Vermont too}

States Borders

First off, most Canadian or American states' borders are not particularly straight. Even when they are supposed to be straight, there are often nooks and crannies.

But indeed there's a tendency to use simple straight borders when creating a territorial entity from scratch, especially on the basis of longitude and latitudes. We see this in many colonial borders, in America or elsewhere in the various European empires. Due to the way map are usually drawn, this often ends up looking like straight lines.

The advantages for doing so are obvious. Decision makers did not often have much details on local geographic features when portioning remote territorial claims into colonies. Even if they did, basing borders on geography was prone to create disputes. The inaccuracy of surveys aside, the natural twists and turns of geographic features, especially rivers (which to make matters worse may change course) are source of major headaches.

For instance, the recently settled long standing dispute between Maine and New Hampshire over islands in the Piscataqua River that forms their borders; Alabama and Georgia's dispute over their Chattahoochee River border; or Georgia and South Carolina's dispute at the Savannah River and its islands.

In contrast, there is only one 42nd parallel (incidentally part of the border between New York and Pennsylvania, which is fixed, simple, and objectively determinable.

Canadian-US Border

This border in particular seems straight because a huge 3,500 km section of the Canadian-US border was somewhat arbitrarily fixed at the 49th parallel. Most of the border west of the Lake of the Woods was first proposed in 1807, and decided in the Anglo-American Convention of 1818, with the Oregon section finalised in the Oregon Treaty.

The 49th parallel had formerly been proposed by Britain as a formal border with French Louisiana as early as the 1713 Treaty of Utrecht. This was revived after Louisiana was purchased as a satisfactory border for both. At the time Louisiana claims include the entirety of the Mississippi's western watershed, while Britain claimed the all of Hudson's Bay drainage basin. Both extended north and south of the 49th parallel, respectively. Setting the border this was, in an appealingly simple (on paper) straight line, was thus an acceptable compromise for both nations.

Most of Alaska's border with Canada was inherited from Russian times. It looks straight because most of it were fixed at the 141st meridian west under the Anglo-Russian Convention of 1825.

Multiple wars might eventually readjust the border to more natural terrain features. However, the reality is that the United States had not fought any war against Canada (or British North America) since the borders were demarcated. Consequently, the border remained as it was drawn when the land was largely devoid of European settlements.

Lastly, if you look closely at the border, there is nothing straight about the Canadian-US border east of the Lake of the Woods.