When someone migrates from one place to another, arrows can be used to display the directionality of that journey, on a large scale. For a video on how to create an arrow, see below.
In Express Maps, there are 2 types of arrows: unidirectional and bidirectional. Both types of arrows can be found in the upper toolbar, shown below.
Select an arrow of your choice from the toolbar. To place an arrow on your map, you will click your mouse. With unidirectional arrows, the first time you click, it should be at the starting point, where the journey begins. The second time you click ends the arrow, where the journey ends. Once placed, a dot will appear in the middle of the arrow, allowing you to curve it.