D3 map tooltips

Question

I'm experimenting with a D3 world map and use this example to build upon: http://techslides.com/demos/d3/worldmap-template.html

Now I would like to achieve a tooltip similar to the one in place for the countries (ie highlight and show name) for the cities plotted onto the map.

So far I have pasted and slightly altered the code for the country-tooltip and tried to connect it to the city date from the csv. This is the later part of the code with original comments and my copy-pasting:

//function to add points and text to the map (used in plotting capitals)
function addpoint(lat,lon,text) {
    var gpoint = g.append("g").attr("class", "gpoint");
    var x = projection([lat,lon])[0];
    var y = projection([lat,lon])[1];

    gpoint.append("svg:circle")
        .attr("cx", x)
        .attr("cy", y)
        .attr("class","point")
        .attr("r", 1.5);

    //conditional in case a point has no associated text
    if(text.length>0){
        gpoint.append("text")       
            .attr("x", x+2)
            .attr("y", y+2)
            .attr("class","text")       
            .text(text);
    }


gpoint

    .on("mousemove", function(d,i) {


        var mouses = d3.mouse(svg.node())
            .map( function(d) { return parseInt(d); } );

        tooltip.classed("hidden", false)
            .attr("style", "left:"+(mouses[0])+"px;top:"+(mouses[1])+"px")  
            .html(d.CapitalName);                                                       
    })


    .on("mouseout",  function(d,i) {
        tooltip.classed("hidden", true);
    }); 

When I now hover over one of the capitals it gives me `Cannot read property 'CapitalName' of undefined.

Can anyone help me?

Answer 1

As I said in my comment,

Have you bound any data to gpoint? It doesn't look like it, so d3 isn't going to pass a datum (the d in your mousemove function). Hence the error: Cannot read property 'CapitalName' of undefined

This is becuase you aren't using d3 data-binding. If I'm reading your code correctly, you are doing something like this:

var myDat = [{lat: 34, lon: 39, CapitalName: "akdjf"}, etc...]
for (var i = 0; i < myDat.length; i++){
   addpoint(myDat[i].lat,myDat[i].lon,myDat[i].CapitalName);
}

d3 though, wants your data bound and then it loops internally. Something like this (totally untested but hope you can get the idea):

d3.csv("data/country-capitals.csv", function(err, capitals) { 

    var gpoint = g.selectAll('.gpoint')
      .data(capitals) //<-- bind your data
      .enter() //<-- enter selection
      .append("g")
      .attr("class", "gpoint");

    gpoint.append("circle")
      .attr("cx", function(d, i){
        return projection([d.lat,d.lon])[0]; //<-- bound data and d is passed in...
      }).attr("cy", function(d, i){
        return projection([d.lat,d.lon])[1];
      });

    gpoint.on("mousemove", function(d,i) {
        var coors = d3.mouse(this);
        tooltip.classed("hidden", false)
          .attr("style", "left:"+(coors.x)+"px;top:"+(coors.y)+"px")  //<- use d3.mosue to get position
          .html(d.CapitalName);  //<-- bound data d is passed...                                                   
        });
}

EDIT FOR COMMENT

Yes, you'll need to convert to numbers. d3 provides a handy callback for it:

d3.csv("data/country-capitals.csv", function(d) {
  return {
    CapitalLongitude = +d.CapitalLongitude,
    CapitalLatitude = +d.CapitalLatitude,
    CapitalName = d.CapitalName
  };
}, function(error, capitals) {
   // rest of code here
});