code: function getAdjustedTileIndex({x, y, z}, adjustedZ) {
    const m = Math.pow(2, z - adjustedZ);
    return {
      x: Math.floor(x / m),
      y: Math.floor(y / m),
      z: adjustedZ
    };
  }
docs: Calculates and returns a new tile index {x, y, z}, with z being the given adjustedZ.