将状态标签和工具提示及其值添加到D3美国地图

Question

随附的屏幕快照显示了以下代码。 我正在绘制每个州的比萨餐厅数量。 我在添加状态标签和向我显示地图上每种状态的对应值的工具提示时遇到了麻烦。 我希望能够将鼠标悬停在一个状态上，然后有一个工具提示，告诉我它是什么状态以及它的价值。 到目前为止，这是我所做的。

<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="utf-8">
<script src="https://d3js.org/d3.v4.min.js"></script>
<style type="text/css">

/* Legend Font Style */
body {
    font: 11px sans-serif;
    background-color: #ffffff;
}

/* Legend Position Style */
.legend {
    position:absolute;
    left:20px;
    top:30px;
}


.axis text {
    font: 10px sans-serif;
}

.axis line, .axis path {
    fill: none;
    stroke: #000;
    shape-rendering: crispEdges;
}



</style>
</head>
<body>
<script type="text/javascript">

//Width and height of map
var width = 960;
var height = 500;

var lowColor = '#f9f9f9'
var highColor = '#bc2a66'

// D3 Projection
var projection = d3.geoAlbersUsa()
  .translate([width / 2, height / 2]) // translate to center of screen
  .scale([1000]); // scale things down so see entire US

// Define path generator
var path = d3.geoPath() // path generator that will convert GeoJSON to             SVG paths
  .projection(projection); // tell path generator to use albersUsa       projection

//Create SVG element and append map to the SVG
var svg = d3.select("body")
  .append("svg")
  .attr("width", width)
  .attr("height", height);

// Load in my states data!
d3.csv("statesdata.csv", function(data) {
    var dataArray = [];
    for (var d = 0; d < data.length; d++) {
        dataArray.push(parseFloat(data[d].value))
    }
    var minVal = d3.min(dataArray)
    var maxVal = d3.max(dataArray)
    var ramp =     d3.scaleLinear().domain([minVal,maxVal]).range([lowColor,highColor])

  // Load GeoJSON data and merge with states data
  d3.json("us-states.json", function(json) {

    // Loop through each state data value in the .csv file
    for (var i = 0; i < data.length; i++) {

      // Grab State Name
      var dataState = data[i].state;

      // Grab data value 
      var dataValue = data[i].value;

      // Find the corresponding state inside the GeoJSON
      for (var j = 0; j < json.features.length; j++) {
        var jsonState = json.features[j].properties.name;

        if (dataState == jsonState) {

          // Copy the data value into the JSON
          json.features[j].properties.value = dataValue;

          // Stop looking through the JSON
          break;
        }
      }
    }

    // Bind the data to the SVG and create one path per GeoJSON feature

    svg.selectAll("path")
      .data(json.features)
      .enter()
      .append("path")
      .attr("d", path)
      .style("stroke", "#fff")
      .style("stroke-width", "1")
      .style("fill", function(d) { return ramp(d.properties.value) });

      g.selectAll("text")
        .data(json.features)
        .enter()
        .append("svg:text")
        .text(function(d){
        return d.properties.name;
        })
        .attr("x", function(d){
        return path.centroid(d)[0];
        })
        .attr("y", function(d){
        return  path.centroid(d)[1];
        })
        .attr("text-anchor","middle")
        .attr('font-size','6pt');

        // add a legend
        var w = 140, h = 300;

        var key = d3.select("body")
            .append("svg")
            .attr("width", w)
            .attr("height", h)
            .attr("class", "legend");

        var legend = key.append("defs")
            .append("svg:linearGradient")
            .attr("id", "gradient")
            .attr("x1", "100%")
            .attr("y1", "0%")
            .attr("x2", "100%")
            .attr("y2", "100%")
            .attr("spreadMethod", "pad");

        legend.append("stop")
            .attr("offset", "0%")
            .attr("stop-color", highColor)
            .attr("stop-opacity", 1);

        legend.append("stop")
            .attr("offset", "100%")
            .attr("stop-color", lowColor)
            .attr("stop-opacity", 1);

        key.append("rect")
            .attr("width", w - 100)
            .attr("height", h)
            .style("fill", "url(#gradient)")
            .attr("transform", "translate(0,10)");

        var y = d3.scaleLinear()
            .range([h, 0])
            .domain([minVal, maxVal]);

        var yAxis = d3.axisRight(y);

        key.append("g")
            .attr("class", "y axis")
            .attr("transform", "translate(41,10)")
            .call(yAxis)
  });

});
</script>
</body>
</html>

谢谢。