Guess which link-map representation above is the most efficient for showing directionality? Information Aesthetics blog has an interesting article about the different techniques for showing the “from-” and “to-” of network charts.
Networks are often visualized using points and interconnecting lines, with triangular arrowheads at one or both ends to show any directionality between the different points. Although such a standard arrow representation seems intuitive, it can lead to problems in dense graphs that contain many incoming or outgoing relationships. Furthermore, since the arrowheads often have approximately the same size and aspect ratio as the small circles they connect, the graph as a whole might be perceived as cluttered with so much visual detail to the point of being distracting.