Plotting points on a map with D3

You have a simple typo in your code -- coordinates should be passed as (longitude, latitude) to the projection, not the other way round. This code should work fine:

 svg.selectAll(".pin")
  .data(places)
  .enter().append("circle", ".pin")
  .attr("r", 5)
  .attr("transform", function(d) {
    return "translate(" + projection([
      d.location.longitude,
      d.location.latitude
    ]) + ")";
  });