Just an historic note. When King Philippe II/III pushed the Treaty of London (1604) down everybody's throat Spanish agents had long been at work throughout North America setting "bench marks" in place for later surveys. They actually placed (or identified) bench marks in Virginia ~ so we know that Spain actually wanted the ability to find the true border with Virginia so that they could later build a large wall with a minefield ~ presumably to keep the Virginians out of New Spain.
There were other boundaries as well.