socket.on('clientReady', () => {
console.log('Data stream to client initiated');
cursor = model.shipModel.find({}).lean().cursor();
cursor.on('data', (doc) => {
  socket.emit('data', doc);
  cursor.pause();
  socket.on('moreData', () => {
    cursor.resume();
  });
});

var mapShips = (ship) => {
  let element = ships.get(ship.MMSI);
  if (typeof element != 'undefined') {
    let latlng = [ship.LAT, ship.LON];
    element.coordinates.push(latlng);
    refreshPolyline(element.shipPolyline, element.coordinates);
  } else {
    let newShip = {};
    newShip.coordinates = [];
    let latlng = [ship.LAT, ship.LON];
    newShip.coordinates.push(latlng);
    newShip.shipPolyline = new L.polyline([latlng], {
      smoothFactor: 1,
      color: color,
      className: 'polylineStyle'
    }).addTo(map);
    ships.set(ship.MMSI, newShip);
  }
};