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)

    })

    if (expand > 0) {

      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

    }

}