Sometimes it's pretty hard to tell where vectors go and not. Especially on big maps. To make it easier to see, we could just add some color to the squares surrounding the vectoring cities/the vectored cities. Green square goes to green circle/whatever, red square goes to red, with the lines colors still as they are, showing how many turns it will take.
Another function that could be added is showing the width of vectoring (illustrated by geometrical shapes). Within the first shape (with the selected city in the middle) is two turns (minimum), within the second shape is three turns etc.
When looking at allied cities no vectoring is showed at all. It says which cities are vectoring if you examine the troops, but there are no lines between the cities on the map.