This is a tricky little bit I've been seeing. Natural borders are great, and rivers (which are so conveniently shown on so many of our basemaps) are the greatest of them all. But, of course, some have cities plonked down on them in a manner which makes it entirely unfeasible for a border to ever be located there (for example, the St Lawrence). I'm not too familiar with some rivers in my native US, let alone the rest of the world - pray tell, what are rivers (erm, on this basemap?) that work as borders.
*I'msorrybutpleasehelpmehereI'mtrulyanignorantswine
*I'msorrybutpleasehelpmehereI'mtrulyanignorantswine