code: function latitudeToPixel (latitude, zoom) {
    const latRad = toRadians(latitude)
    return (1 -
      Math.log(Math.tan(latRad) + (1 / Math.cos(latRad))) /
        Math.PI) / 2 * zScale(zoom)
  }
docs: Convert a latitude to it's pixel value given a `zoom` level.
  
  @param {number} latitude
  @param {number} zoom
  @return {number} pixel
  @example
  var yPixel = lonlat.latitudeToPixel(40, 9) //= 49621.12736343896