Accepted answer

I think it is, as you suggest, a problem with the numbers getting parsed as Strings rather than Numbers. Even if that's not what's breaking it, it'd be good to fix. This is one way of doing it (might be a more idiomatic way to do it, dunno):

var vertices = d3.csv.parseRows(
  function(pt) { return [parseFloat(pt[0]), parseFloat(pt[1])]; })

That might fix your problem.

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