code: function touchstart(e) {
      var i = -1,
          n = e.touches.length,
          t = Date.now();
  
      // doubletap detection
      if ((n == 1) && (t - last < 300)) {
        var z = map.zoom();
        map.zoomBy(1 - z + Math.floor(z), map.mouse(e.touches[0]));
        e.preventDefault();
      }
      last = t;
  
      // store original zoom & touch locations
      zoom = map.zoom();
      angle = map.angle();
      while (++i < n) {
        t = e.touches[i];
        locations[t.identifier] = map.pointLocation(map.mouse(t));
      }
    }
docs: touch identifier -> location