使用d3和topojson绘制地图

Question

I try to draw a map thank to d3 and topojson. Then I draw each country one by one with this code :

d3.json("datamaps-0.5.0/src/js/data/world.topo.json", function(error, map) {
    console.log(map);
    for (i=0; i<map.objects.world.geometries.length; i++)
    {
    svg.append("path")
            .attr("class", "state")
        .datum(topojson.feature(map, map.objects.world.geometries[i]))
        .attr("d", path);
    }
});

Although the code works well, I'm looking for a more elegant way than a loop to draw a such map...

Answer 1

One way to do it is to first compute your data array, then map it to the paths with d3

 var features= map.objects.world.geometries
                  .map( //.map: create a new array by applying the function below to each element of the orignal array
                        function(g) { //take the geometry
                          return topojson.feature(map, g) //and return the corresponding feature.
                        }
                      );
 svg.selectAll(".state")
    .data(features)
    .enter()
    .append("path")
    .attr("class", "state")
    .attr("d", path);

This should be exactly equivalent to your code.