code: function _calculateGridLatLonOffset(cellSize, latitude) {
    const yOffset = _calculateLatOffset(cellSize);
    const xOffset = _calculateLonOffset(latitude, cellSize);
    return {yOffset, xOffset};
  }
docs: calculate grid layer cell size in lat lon based on world unit size
  and current latitude
  @param {number} cellSize
  @param {number} latitude
  @returns {object} - lat delta and lon delta