code: function pixelToLatitude (y, zoom) {
    var latRad = Math.atan(Math.sinh(Math.PI * (1 - 2 * y / zScale(zoom))))
    return toDegrees(latRad)
  }
docs: Convert a pixel to it's latitude value given a zoom level.
  
  @param {number} y
  @param {number} zoom
  @return {number} latitude
  @example
  var lat = lonlat.pixelToLatitude(50000, 9) //= 39.1982053488948