Edges Example 6 for How to Create Effective Network Data Visualization
Rather than representing directionality of each edge, it might make more sense to represent whether a tie is reciprocated, which is a product of directionality. Reciprocity indicates stronger ties and might be more important to an audience than explicit direction of connections.
The method for calculating reciprocity is simply to create a hash of edge IDs and check when each is evaluated to see if the reverse of that edge has already been added to the array.
Obviously, this should also have a legend, because every data visualization should have a legend.