they are defined by rivers, ridges, Coastlines or lines not parallel to lines of latitude and longitude. Examples of states like this are: Washington D.C. (almost diamond shape), New Jersey and Hawaii (undefined territorial waters)
Probably a river. And the need for a feature to define the line "on a map" is
of very minor importance. The map only shows what was worked out, defined,
and agreed to by the people around there. The need for a feature to clearly
define the limits of the land was almost always driven mainly by the families
who wanted the opportunity to farm the rich land adjacent to the river.
When longitude and latitude are not used, a river is most often used to define a state border.
Every point on Earth has longitude and latitude.
The Colombia/Brazil border
No, no more than border lines between states or naions.
States with only straight borders could probably be defined just by longitude and latitude. Those states are: Utah, Wyoming, Colorado, and New Mexico - so 4 states. Colorado and Wyoming would be easiest since they are both essentially rectangles projected onto the sphere of the Earth. Utah is a little more complicated since Wyoming bites into one corner of the state. New Mexico would require the most latitude/longitude information since its Southern border is kind of jagged. All the other states have at least one border determined by a coastline or river or mountain range or some other feature that is most definitely NOT straight, thus cannot be accurately captured just by longitude and latitude.
That's very near the border between Siberia and North Korea
Every point on Earth has longitude and latitude.
One can learn about this specific border crossing on many websites online. Wikipedia provides detailed information regarding this border and where the exact location is on the longitude and latitude line.
A geometric border is made by the lines of latitude and longitude, the United States has mostly a goemetric border with Canada.
The Colombia/Brazil border
No, no more than border lines between states or naions.
States with only straight borders could probably be defined just by longitude and latitude. Those states are: Utah, Wyoming, Colorado, and New Mexico - so 4 states. Colorado and Wyoming would be easiest since they are both essentially rectangles projected onto the sphere of the Earth. Utah is a little more complicated since Wyoming bites into one corner of the state. New Mexico would require the most latitude/longitude information since its Southern border is kind of jagged. All the other states have at least one border determined by a coastline or river or mountain range or some other feature that is most definitely NOT straight, thus cannot be accurately captured just by longitude and latitude.
That's very near the border between Siberia and North Korea
The southern-most latitude in Canada is 41°N and the majority of the US/Canada border is at 49°N latitude (also called the 49th parallel) from 95°W to 123°W longitude.
On the Arctic Circle, near the border between Finland and Russia.
it ran across the border of Mexico
The latitude and longitude of Lake Titicaca is 15.7500-degrees south, 69.4167-degrees west. Lake Titicaca is located in the Andes on the border of Peru and Bolivia.
The border separating US and Canada and Washington, USA and Vancouver, Canada.