In d3.js map, points are hidden behind other features - d3.js

Question

I have tried to create a map of India with some points in it. I followed the codebase from here.
Everything is fine except the points. They are hidden behind other features on the map, and because of this are not visible. How do I layer the features so that the points are visible?

Answer 1

In d3.js map layering can be handled in two ways. If this is your code (paraphrasing from your example)
d3.json("path.json",function (json) {
g.selectAll("path")
.data(json.features)
.enter().append("path")
.attr("d", path);
});
d3.csv("path.csv",function (csv) {
g.selectAll("circle")
.data(csv)
.enter().append("circle")
.attr("cx", function(d) { projection([d.x,d.y])[0] })
.attr("cy", function(d) { projection([d.x,d.y])[1] })
.attr("r",4);
});
Data will be added to the 'g' element based on the order in which the callback functions are completed, so it is possible that the csv data will be drawn first and the json data will be drawn after it.
The first method I'll present here is the cleanest way in most situations to specify data layer order (in my mind). SVG 'g' elements are appended in the order that they are specified. This gives you easy control over the layering of data:
var gBackground = svg.append("g"); // appended first
var gDataPoints = svg.append("g"); // appended second
// ... and so forth
Then, all you have to do is specify to which 'g' element/layer data gets appended/inserted into. So, your code would look more like:
d3.json("path.json",function (json) {
gBackground.selectAll("path")
.data(json.features)
.enter().append("path")
.attr("d", path);
});
d3.csv("path.csv",function (csv) {
gDataPoints.selectAll("circle")
.data(csv)
.enter().append("circle")
.attr("cx", function(d) { projection([d.x,d.y])[0] })
.attr("cy", function(d) { projection([d.x,d.y])[1] })
.attr("r",4);
});
The second option appends data to the same 'g' element but ensures the order in which this is done is controlled, by drawing the second layer in the callback function that draws the first, after the first is drawn:
To control the ordering of the data with this method we would modify the code to something like:
d3.json("path.json",function (json) {
g.selectAll("path")
.data(json.features)
.enter().append("path")
.attr("d", path);
// once the json is drawn, draw the csv:
d3.csv("path.csv",function (csv) {
g.selectAll("circle")
.data(csv)
.enter().append("circle")
.attr("cx", function(d) { projection([d.x,d.y])[0] })
.attr("cy", function(d) { projection([d.x,d.y])[1] })
.attr("r",4);
});
});