borders

i have been looking at borders lately. i'm doing this project at work that requires me to find remote radio antenna locations. sometimes there are addresses listed, but often i only have a set of gps coordinates. using google earth this usually gets me right in the backyard, but sometimes it pins a position quite a distance away. as i went through my list of sites sometimes i would notice "nad27" before listing the coordinates. most of ours use nad83. a little bit of research showed me the nad27 model was created in the 1800's by a survey team that traversed the entire north american continent and was based on an ellipsoid.
in the 1980's satellite mapping technology revealed that earth was not as perfect an ellipse as originally suspected and thus a new more accurate model was created. and even today there is a another model called wgs84 using the center of the earth as reference. so what does all this mean?
interestingly, as we travel around the country and pass from one state into another, these borders may have shifted. often as much as the length of a football field or more. the invisible lines we have drawn on maps to establish fences have been re-staked. all those folks who made trips to the four corners states as kids and stuck a hand and foot in four different states at once may have only been bending over in utah.
and this got me to thinking about what is it that actually creates a border anyway? if you look at a map of the united states, those early established states are often separated by natural borders like rivers, ocean and mountain ranges. this it seems to me is an idea that makes the most sense. but when you get into areas like kansas and nebraska where it's all just rolling flatland, then what? i guess since there's no more land to discover and draw new lines on we'll just keep erasing the old and re-drawing new ones.