What do the blue lines on the Civilization 6 map mean? For instance, in this question, there is a blue line immediately to the north-northwest of Mbanza Kongo. What does it mean?
When selecting a unit that can move, the blue line is representing the spaces that the selected unit can move to in the current turn. It is usually 2 spaces but eventually with roads and other era upgrades you can move further in one turn.
The farthest space out is the farthest they can go but you don't have to use up all the movement (go as far in the blue line) as possible if you don't want to.