Create an SVG element to hold the map
var svg = d3.select("body").append("svg")
  .attr("width", 500)
  .attr("height", 500);

// Create a geographic projection
var projection = d3.geoMercator()
  .center([0, 0])
  .scale(100)
  .translate([250, 250]);

// Create a path generator
var path = d3.geoPath()
  .projection(projection);

// Add a circle to the center of the map
svg.append("path")
  .datum({type: "Point", coordinates: [0, 0]})
  .attr("d", path)
  .attr("fill", "red")
  .attr("stroke", "black");