you see, Mateusz, the point is that we're here looking at a copy from the maps of the National Geographic Institute, reverse engingeered as if interpreting a textual description, and if the textual description says that the border follows the river, then the river is made to follow the border, to its extreme consequences. then hikers will find themselves with a worthless map in their hands and navigator. Alvarado's concern is "political borders", not hikers, not maps.