Tooltip

<!DOCTYPE html>

body {
		font-family: arial, sans;
		font-size: 9px;
		width: 960px;
		margin: 0px auto;
	}

.axis path {
		display: none;
	}
	.axis line {
		stroke-width: 1px;
		stroke: #ccc;
		stroke-dasharray: 5px 3px;
		shape-rendering: crispEdges;
	}

/*important for tooltip positioning*/
	.primaryContainer {
		position: relative;
	}
	.graphicContainer {
		max-width: 960px;
		position: relative;
	}

/*tooltip*/
	.show {
		display: block;
	}
	.hidden {
		display: none;
	}
	.tooltip {
		background-color: #333;
		padding: 4px 8px;
		position: absolute;
		color: #fff;
		opacity: 0.8;
		z-index: 100;
	}
	g.container circle:hover {
		cursor: pointer;
	}

/*voronoi*/
	.voronoiPath {
		fill: none;
		stroke: #f0f;
		/*here's the trick*/
		pointer-events: all;
	}
	.voronoiPath:hover {
		cursor: pointer;
	}

</style>
</head>

<body>

</body>

var margin = {top: 20, right: 20, bottom: 20, left: 40};
var width = 960 - margin.left - margin.right,
	height = 500 - margin.top - margin.bottom;

var xScale = d3.scale.linear()
	.range([0,width]);
var yScale = d3.scale.linear()
	.range([height,0]);

var xAxis = d3.svg.axis()
	.scale(xScale)
	.orient("bottom");
var yAxis = d3.svg.axis()
	.scale(yScale)
	.tickSize(-width)
	.orient("left");

var svg = d3.select("body").append("svg")
	.attr("width", width + margin.left + margin.right)
	.attr("height", height + margin.top + margin.bottom)
	.append("g")
	.attr("transform", "translate(" + margin.left + "," + margin.top + ")");

// tooltip begins here
var tooltip = d3.select('.tooltip');
	tooltip.append('div').attr('class', 'ttInfo');
var tooltipText = d3.select('.ttInfo');

d3.tsv("group1.tsv", ready);

function ready(error, data) {
	if (error) return console.warn(error);

data.forEach(function(d) {
		d.x = +d.x;
		d.y = +d.y;
	});

xScale.domain(d3.extent(data, function(d) { return d.x; }));
	yScale.domain(d3.extent(data, function(d) { return d.y; }));

svg.append("g")
		.call(xAxis)
		.attr("class", "axis xAxis")
		.attr("transform", "translate(0," + height + ")");
	svg.append("g")
		.call(yAxis)
		.attr("class", "axis yAxis");

// enter the mystical voronoi
	var voronoi = d3.geom.voronoi()
		.clipExtent([[0, 0], [width, height]]);

// there may be a more elegant way to build verticies, but I'm not sure
	var vertices = [
	];
	data.forEach( function (d) {
		var x = xScale(d.x);
		var y = yScale(d.y);
		var vert = [x,y];
		vertices.push(vert);
	});

var voronoiPath = svg.append("g").selectAll("path.voronoiPath")
		.data(voronoi(vertices), polygon)
		.enter()
		.append("path")
		.attr("class", "voronoiPath")
		.attr("d", polygon)
		.on('mouseover', renderTooltip);

function polygon(d) {
		return  "M" + d.join("L") + "Z";
	};

function renderTooltip () {
		console.log("New Voronoi")
	};

dataGroup.append('circle')
		.attr('r', 3);
	
}

</script>

https://cdnjs.cloudflare.com/ajax/libs/d3/3.5.5/d3.min.js