function bounds(positions = [], expand = 0) {    let minLng = 180    let minLat = 90    let maxLng = -180    let maxLat = -90    positions.forEach(item => {      minLng = Math.min(minLng, item.lng || item.x)      minLat = Math.min(minLat, item.lat || item.y)      maxLng = Math.max(maxLng, item.lng || item.x)      maxLat = Math.max(maxLat, item.lat || item.y)    })    ) {
      let diffLng = Math.abs(maxLng - maxLng)
      let diffLat = Math.abs(maxLat - minLat)
      minLng -= diffLng * expand
      minLat -= diffLat * expand
      maxLng += diffLng * expand
      maxLat += diffLat * expand
    }
    return {
      west: minLng,
      south: minLat,
      east: maxLng,
      north: maxLat
    }
}