Graphics Reference
In-Depth Information
Link Shape
Links are almost always represented as lines but, like nodes, can also vary in
form. One common variation is that you can draw them as either curved or
straight lines.
Straight lines point directly from one node to the other, which makes it
a little easier to see where they are headed when focused on or zoomed
into one of the nodes. In a geographic layout, for example, this can imply
a destination, even when the destination cannot be seen. Straight lines can
also be drawn more quickly, so in a graph with a lot of links, straight lines
will perform better.
Curved lines, on the other hand, are less likely to completely obscure each
other. A short line and long line in the same path will be easier to see
because their arcs will follow a different path. Curved lines also
communicate directionality, if the links have a direction. Typically, you use
a clockwise arc, so clockwise swoops indicate the direction of flow. A link
from A to B and one from B to A will also disentangle nicely when they are
curved, providing the capability for you to express different weights in each
direction.
Tip
Try curved links unless the number of them is so high that drawing
them all is too slow. Unless the graph is geospatial, this will almost
always produce clearer results, and the curved links can be used to
communicate directionality.
Directional Indication
Clockwise arcs are a great base-level indication of direction. You can also
add arrowheads for clearer self-expression, but only when you have few
links to display. Otherwise, they will create too much visual clutter. A third
option is to use tapered links, which resemble arrowheads that span the
complete distance from source to destination node. Tapered links can
indicate direction along their whole length.
However, it's good to keep in mind that if directionality is important in
a graph and the graph is big enough that arrows are no longer easily
perceived, you should consider techniques other than link representation,
like those documented in Chapter 12. More often, directionality is present in
