d3.js map with markers

Easy example on how to put marker on a d3.js map.

You got 2 options:

using d3.geo.path() which does all the work for you
using svg circles and translating them via projection(d.geometry.coordinates)

<!DOCTYPE html>
<meta charset="utf-8">
<style>

.graticule {
  fill: none;
  stroke: #777;
  stroke-opacity: .5;
  stroke-width: .5px;
}

.land {
  fill: #222;
}

.boundary {
  fill: none;
  stroke: #fff;
  stroke-width: .5px;
}

circle {
  fill: yellow;
}

.geopath {
  fill: green;
}

</style>
<body>
<script src="https://d3js.org/d3.v3.min.js"></script>
<script src="https://d3js.org/topojson.v1.min.js"></script>
<script>

var width = 1200,
    height = 720;

var projection = d3.geo.mercator()
    .scale(8000)
    .precision(.1)
    .center([13.320255,52.52831499])
    .translate([width / 2, height / 2])

var path = d3.geo.path()
    .projection(projection);

var graticule = d3.geo.graticule();

var svg = d3.select("body").append("svg")
    .attr("width", width)
    .attr("height", height);

svg.append("path")
    .datum(graticule)
    .attr("class", "graticule")
    .attr("d", path);

d3.json("world-50m.json", function(error, world) {
  svg.insert("path", ".graticule")
      .datum(topojson.feature(world, world.objects.land))
      .attr("class", "land")
      .attr("d", path);

svg.insert("path", ".graticule")
      .datum(topojson.mesh(world, world.objects.countries, function(a, b) { return a !== b; }))
      .attr("class", "boundary")
      .attr("d", path);
});

d3.json("stops_berlin.geojson", function(error, data) {

// using d3.geo.path() which does all the work for you
  svg.append("path")
    .datum(data)
    .classed("geopath", true)
    .attr("d", path)

// or insert your own custom dots by hand
  svg.append("g")
    .selectAll("g")
    .data(data.features)
    .enter()
      .append("g")
      .attr("transform", function(d) { return "translate(" + projection(d.geometry.coordinates) + ")"; })
      .append("circle")
      .attr("r", 1)

});

d3.select(self.frameElement).style("height", height + "px");
  
</script>

Modified http://d3js.org/d3.v3.min.js to a secure url

Modified http://d3js.org/topojson.v1.min.js to a secure url

https://d3js.org/d3.v3.min.js

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