rveciana - d3-tutorial-v-adding-tooltips
D3 tutorial V: Adding tooltips

This example belongs to the presentation made to the OSGeo local group in Barcelona Geoinquiets The example is an adaptation from Mike Bostock’s Symbol Map example
<!DOCTYPE html>
<meta charset="utf-8">
<style>

.states {
  fill: #ccc;
  stroke: #fff;
}

.symbol {
  fill: steelblue;
  fill-opacity: .8;
  stroke: #fff;
}

.tooltip{ background-color:rgba(68,136,187,0.5);;
          margin: 10px;
          height: 50px;
          width: 150px;
          padding-left: 10px; 
          padding-top: 10px;
    -webkit-border-radius:10px;
    -moz-border-radius:10px;
    border-radius:10px;
        }
</style>
<body>
<button type="button" id="change">Change</button>

<script src="http://d3js.org/d3.v3.min.js"></script>
<script src="http://d3js.org/topojson.v0.min.js"></script>
<script src="http://d3js.org/queue.v1.min.js"></script>
<script type="text/javascript" src="./tooltip.js"></script>


<script>
var width = 960,
    height = 500;
var states, points;


var radius = d3.scale.sqrt()
    .domain([0, 1e6])
    .range([0, 10]);

var projection = d3.geo.mercator()
    .center([-97, 37])
    .scale(4000 / 2 / Math.PI)
    .translate([width / 2, height / 2]);


var path = d3.geo.path()
.projection(projection);

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

queue()
    .defer(d3.json, "/mbostock/raw/4090846/us.json")
    .defer(d3.json, "/mbostock/raw/3750900/us-state-centroids.json")
    .await(ready);


function ready(error, us, centroid) {
states = svg.append("path")
      .attr("class", "states")
      .datum(topojson.object(us, us.objects.states))
      .attr("d", path);

    points =  svg.selectAll(".symbol")
      .data(centroid.features.sort(function(a, b) { return b.properties.population - a.properties.population; }))
    .enter().append("path")
      .attr("class", "symbol")
      .attr("d", path.pointRadius(function(d) { if(d.properties) { return radius(d.properties.population);} else {return;} }))
      .call(d3.helper.tooltip(
        function(d, i){
          return "<b>"+d.properties.name + "</b><br/>pop: "+d.properties.population;
        }
        ));
};

d3.select("#change").on("click", function() {
  projection = d3.geo.albers();
  path.projection(projection);
  states.transition()
      .duration(10000)
      .attr("d", path);
  points.transition()
      .duration(3000)
      .attr("d", path);
});


</script>