code: function renderToContext (geoJson, projection) {
      var shapePath = new THREE.ShapePath();
      var mapRenderContext = new ThreeJSRenderContext(shapePath);
      var mapPath = geoPath(projection, mapRenderContext);
      mapPath(geoJson);
      return mapRenderContext;
    }
docs: Takes the input geoJson and uses the projection and D3 to draw it
  into a ThreeJSRenderContext.
  
  @param geoJson the geoJson object to render
  @param projection the projection to use for rendering
  @return ThreeJSRenderContext