jtibbutt/data.json

## data.json
{
"nodes":[
{"name":"United Kingdom","group":0},
{"name":"France","group":0},
{"name":"Germany","group":0},
{"name":"Italy","group":0},
{"name":"Spain","group":0}
],
"links":[
{"source":0,"target":1,"value":3},
{"source":0,"target":2,"value":2},
{"source":0,"target":3,"value":1},
{"source":1,"target":0,"value":2},
{"source":1,"target":2,"value":3},
{"source":1,"target":4,"value":1},
{"source":2,"target":0,"value":3},
{"source":2,"target":1,"value":2},
{"source":2,"target":3,"value":1},
{"source":3,"target":0,"value":3},
{"source":3,"target":2,"value":1},
{"source":3,"target":4,"value":2},
{"source":4,"target":0,"value":3},
{"source":4,"target":1,"value":1},
{"source":4,"target":3,"value":2}
]
}

## index.html
<!DOCTYPE html>
<meta charset="utf-8">
<style>

.node {
stroke: #fff;
stroke-width: 1.5px;
}

.link {
stroke: #999;
stroke-opacity: .2;
}

</style>
<body>
<script src="http://d3js.org/d3.v3.min.js"></script>
<script>

var width = 960,
height = 500;

var color = d3.scale.category20();

var force = d3.layout.force()
.charge(-400)
.linkDistance(100)
.size([width, height]);

var svg = d3.select("body").append("svg")
.attr("width", width)
.attr("height", height);

d3.json("data.json", function(error, graph) {
force
.nodes(graph.nodes)
.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.name; });

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>
</body>
</html>
	{
	"nodes":[
	{"name":"United Kingdom","group":0},
	{"name":"France","group":0},
	{"name":"Germany","group":0},
	{"name":"Italy","group":0},
	{"name":"Spain","group":0}
	],
	"links":[
	{"source":0,"target":1,"value":3},
	{"source":0,"target":2,"value":2},
	{"source":0,"target":3,"value":1},
	{"source":1,"target":0,"value":2},
	{"source":1,"target":2,"value":3},
	{"source":1,"target":4,"value":1},
	{"source":2,"target":0,"value":3},
	{"source":2,"target":1,"value":2},
	{"source":2,"target":3,"value":1},
	{"source":3,"target":0,"value":3},
	{"source":3,"target":2,"value":1},
	{"source":3,"target":4,"value":2},
	{"source":4,"target":0,"value":3},
	{"source":4,"target":1,"value":1},
	{"source":4,"target":3,"value":2}
	]
	}
	<!DOCTYPE html>
	<meta charset="utf-8">
	<style>

	.node {
	stroke: #fff;
	stroke-width: 1.5px;
	}

	.link {
	stroke: #999;
	stroke-opacity: .2;
	}

	</style>
	<body>
	<script src="http://d3js.org/d3.v3.min.js"></script>
	<script>

	var width = 960,
	height = 500;

	var color = d3.scale.category20();

	var force = d3.layout.force()
	.charge(-400)
	.linkDistance(100)
	.size([width, height]);

	var svg = d3.select("body").append("svg")
	.attr("width", width)
	.attr("height", height);

	d3.json("data.json", function(error, graph) {
	force
	.nodes(graph.nodes)
	.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.name; });

	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>
	</body>
	</html>