Node-Link diagram

##Insight gained:

South Atlantic region has more number of states and are represented by light green color.
Mid Atlantic region has less number of states and are represented by violet color.
The state ME (maine) has only one connection i.e, to NH (New Hampshire).

<!DOCTYPE html>
<meta charset="utf-8">
<style>
.node {
  stroke: #fff;
  stroke-width: 1.5px;
}
.link {
  stroke: #999;
  stroke-opacity: .6;
}
</style>
<body>
<script src="//d3js.org/d3.v3.min.js"></script>
<script>
var width = 960,
    height = 500;
var color = d3.scale.category20();
var force = d3.layout.force()
    .charge(-120)
    .linkDistance(30)
    .size([width, height]);
var svg = d3.select("body").append("svg")
    .attr("width", width)
    .attr("height", height);
d3.json("data.json", function(error, graph) {
  if (error) throw error;
  force
      .nodes(graph.nodes)
      .links(graph.links)
      .start();
  var link = svg.selectAll(".link")
      .data(graph.links)
    .enter().append("line")
      .attr("class", "link")
      .style("stroke-width", function(d) { return Math.sqrt(d.value); });
  var node = svg.selectAll(".node")
      .data(graph.nodes)
    .enter().append("circle")
      .attr("class", "node")
      .attr("r", 10)
      .style("fill", function(d) { return color(d.group); })
      .call(force.drag);
  node.append("title")
      .text(function(d) { return  d.abbr });
  force.on("tick", function() {
    link.attr("x1", function(d) { return d.source.x; })
        .attr("y1", function(d) { return d.source.y; })
        .attr("x2", function(d) { return d.target.x; })
        .attr("y2", function(d) { return d.target.y; });
    node.attr("cx", function(d) { return d.x; })
        .attr("cy", function(d) { return d.y; });
  });
});
</script>

https://d3js.org/d3.v3.min.js