function constructMapboxUrl (tileset) {
  var mapboxAccessToken = config.mapbox_access_token()
  var isRetina = window.devicePixelRatio > 1 ? '@2x' : ''
  return `https://api.mapbox.com/styles/v1/${tileset}/tiles/256/{z}/{x}/{y}${isRetina}?access_token=${mapboxAccessToken}`
}