D3.js, SVG, and force graph

My graph example

by b_long

HTML

<script src="//cdnjs.cloudflare.com/ajax/libs/d3/3.4.11/d3.min.js"></script>
<!-- 
Forked / based on https://jsfiddle.net/yaprak/422mjtu6/1/ 
-->
<div id="graph" style="width: 600px;height: 390px;padding:0px;border: 1px solid gray">
</div>
<div id="another-div">Some other content</div>

CSS

/* CSS from our application */
.node {
  stroke: #222;
  stroke-width: 1.5px;
  fill: #3588cd;
}

.link {
  stroke: #999;
  stroke-opacity: .6;
  stroke-width: 1px;
}

.linklabels {
  font-size: 10px;
}

JavaScript

/*
Note: When declaring mock data, you MUST not have 'links' which
reference a non-existent node.  For example, here we have 5 nodes
meaning that we can access nodes[0] through nodes[4], since 
the array is zero-indexed.  If you attempt to access nodes[5], an
error will be thrown like:

	TypeError: Cannot read property 'weight' of undefined

 I've seen this error, and also it is described by a StackOverflow
	member:
		https://stackoverflow.com/a/22428106
*/
var mock_data = {
  "nodes": [
    {
      "title": "1959",
      "label": "Collection",
      "data": {
        "name": "1959",
        "wikipedia_url": "https://en.wikipedia.org/wiki/1959",
        "Type": "YEAR"
      }
   
    },
    {
      "title": "Buffalo Bills",
      "label": "Collection",
      "data": {
        "name": "Buffalo Bills",
        "wikipedia_url": "https://en.wikipedia.org/wiki/Buffalo_Bills",
        "Type": "ORGANIZATION"
      }
    },
    
    {
      "title": "New Orleans Saints",
      "label": "Collection",
      "data": {
        "name": "New Orleans Saints",
        "wikipedia_url": "https://en.wikipedia.org/wiki/New_Orleans_Saints",
        "Type": "ORGANIZATION"
      }
     },
    {
      "title": "Buffalo",
      "label": "Collection",
      "data": {
        "name": "Buffalo",
        "wikipedia_url": "https://en.wikipedia.org/wiki/Buffalo,_New_York",
        "Type": "LOCATION"
      }
    },{
      "title": "Kiko Alonso",
      "label": "Collection",
      "data": {
        "name": "Kiko Alonso",
        "wikipedia_url": "https://en.wikipedia.org/wiki/Kiko_Alonso",
        "Type": "PERSON"
      }
      
      }
  ],
  "links": [{
      "source": 1,
      "target": 0,
      "relationShip": "established"
    },
    {
      "source": 1,  // Buffalo Bills
      "target": 3, // Buffalo, NY
      "relationShip": "located in"
    },
    {
      "source": 1,  // Buffalo Bills
      "target": 2,  // New Orleans Saints
      "relationShip": "competes against"
    },
    {
     ...