test

<!DOCTYPE html>
<meta charset="utf-8">
<style>
    .province {
        fill: #000;
        stroke: #fff;
        stroke-width: 1px;
    }
    .province:hover {
        fill: #666;
    }
    .hidden {
        display: none;
    }
    div.tooltip {
        color: #222;
        background-color: #fff;
        padding: .5em;
        text-shadow: #f5f5f5 0 1px 0;
        border-radius: 2px;
        opacity: 0.9;
        position: absolute;
    }
</style>
<body>
    <script src="https://d3js.org/d3.v4.min.js"></script>
    <script src="https://d3js.org/topojson.v1.min.js"></script>
    <script>
      
        var width = 690,
            height = 580;
        var svg = d3.select('body').append('svg')
            .attr('width', width)
            .attr('height', height);
        var tooltip = d3.select('body').append('div')
            .attr('class', 'hidden tooltip');
        d3.json('regions.json', function(err, can) {
            if (err) return console.error(err);
          
            var projection = d3.geoConicConformal()
            	.center([2.454071,46.279229])
            	.scale(2800);
               
            var path = d3.geoPath()
                .projection(projection);
          	
          	d3.csv("GrippeFrance2014.csv", function(data) {
    				color.domain([0, 2000]);

d3.json("regions.json", function(json) {
     				//On fusionne les donnees avec le GeoJSON des regions
     				for (var i = 0; i < data.length; i++) {
      			...
      			}

svg.selectAll("path")
      			...
        			.style("fill", function(d) {
              			var value = d.properties.value;
              			...
      						});
    				});
				});
          
            var provinces = svg.selectAll('.province')
                .data(can.features).enter();
            provinces.append('path')
                .attr('class', function(d) {
                    return 'province ' + d.properties.CODE;
                })
                .attr('d', path)
                .on('mousemove', function(d) {
                    var mouse = d3.mouse(svg.node()).map(function(d) {
                        return parseInt(d);
                    });
                    tooltip.classed('hidden', false)
                        .attr('style', 'left:' + (mouse[0] + 15) +
                                'px; top:' + (mouse[1] - 35) + 'px')
                        .html(d.properties.NAME);
                })
                .on('mouseout', function() {
                    tooltip.classed('hidden', true);
                });
        });
    </script>
    </body>

https://d3js.org/d3.v4.min.js

https://d3js.org/topojson.v1.min.js