champagne anarchist | armchair activist

How to make a d3js force layout stay within the chart area - even with multiple components

For a post on analysing networks of corporate control, I wanted to create some network graphs with d3.js. The new edition of Scott Murray’s great book on d3.js, which is updated to version 4, contains a good example to get you started. However, I was still struggling with some practical issues, as the chart below illustrates (reload the page to see the problem develop).

A large part of the graph drifts out of the chart area, and the problem only gets worse on a mobile screen. But I figured out some sort of solution.

As Murray explains, you can vary the strength value of the force layout. Positive values attract, negative values repel. The default value is –30. You could set d3.forceManyBody().strength(-3) to create a more compact graph.

Of course, the ideal setting will depend on screen size. You could vary the strength value according to screen width. While you’re at it, you may also want to vary the radius of nodes and the stroke-width of edges. For example with something like this:

if(w > 380){
    var strength = -3;
    var r = 3;
    var sw = 0.3;
}
else{
    var strength = -1;
    var r = 3;
    var sw = 0.15;
}

Now this may make the graph more compact, but it doesn’t solve one specific problem: components not connected to the rest of the chart will still drift out of the chart area. In my example, there are four components: a large one, and three pairs of nodes that are only connected to each other and not to the rest of the graph.

The way in which I dealt with this was to create four different graphs and attach the small components to a forceCenter at the margin of the chart area. For example, d3.forceCenter().x(0.1 * w).y(0.9 * h)) will put one of them in the bottom left corner. Here’s the result:

It’s still a lot of code - I can’t help feeling there should be a more efficient way to do this. Also, it’s slightly weird that the small components immediately freeze, whereas the large one takes its time to develop into its final shape. And the text labels could be improved. But at least it seems to work.

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