 1: 1,
    // Level 1
    2:  2,
    32: 2,
    // Level 2
    4:  3,
    64: 3,
    // Level 3
    8:   4,
    128: 4,
    // Level 4
    16: 5,
};

var margin = {top: 20, right: 30, bottom: 30, left: 40};
var width  = 800 - margin.left - margin.right;
var height = 150 - margin.top - margin.bottom;

// We keep all the per-chart data in this dictionary.
var chartdata = {};

// Initialize the chart as soon as the page is ready
// The chart hierarchy is:
// #node_chunks_i
// -- g              = chart
// ---- 