code: function boundEdges (points, edges) {
    var bounds = new Array(edges.length)
    for (var i = 0; i < edges.length; ++i) {
      var e = edges[i]
      var a = points[e[0]]
      var b = points[e[1]]
      bounds[i] = [
        nextafter(Math.min(a[0], b[0]), -Infinity),
        nextafter(Math.min(a[1], b[1]), -Infinity),
        nextafter(Math.max(a[0], b[0]), Infinity),
        nextafter(Math.max(a[1], b[1]), Infinity)
      ]
    }
    return bounds
  }
docs: Convert a list of edges in a pslg to bounding boxes