But when I was a surveyor's assistant we usually tried to close surveys to less than an inch. We were really, really, precise about locations. Maybe that was just a weird firm, but I suspect not, I think that's SOP. Given that we placed markers that precise, it is hard to imagine that the physical structures, items, etc got placed more than a couple inches off.
I can't imagine roadways would be much different.
So ya, as you say, these things are known pretty precisely. Turns out that even pre-GPS you could get really good measurements, if you did it right.
Also having done that, it makes me think all the metric stuff is a little silly. It really isn't that hard to go back and forth. Most contracts were in US units, however some government contracts were in metric. So what did we do? Switched the digital theodolite and computer to metric and worked with that.
Really metric only shines when you talk science or engineering, when you are doing more advanced things like inter-unit conversion. There the standardization is so damn useful, hence why science, including in the US, is done and taught in metric (or at least it was when I went to school).
For every day use though? It doesn't really matter. All that matters is you have a feel for the units, and you can have that for both no problem. I really can't see what the compelling reason to convert to metric for everyday use is. Even in countries that have converted, you find plenty of unit mixture. In Canada you will see things at grocers sold in pounds, gallons, etc. It is amusing that in the same grocer you can see meats side by side, some priced by pound, some by 100 grams.
Then all over you find some units that defy either system. Like ever buy a home AC? They are sized in "tons" however if you've had a look at the unit you realize that it is far lighter than the figure. So what the hell does that mean? It means how many tons of ice per day you'd need to equal the cooling capacity. Seriously. It started way back in the day when it was a new concept, and that was a comparable method of measure.
I really think people make a bigger deal of this than is warranted. I certainly don't think there should be any resistance to using the metric system, it is great, but in terms of forcing a conversion, I fail to see what that gains you.