code: def _meters_per_pixel(zoom, lat=0.0, tilesize=256):
      
      return (math.cos(lat * math.pi / 180.0) * 2 * math.pi * 6378137) / (
          tilesize * 2 ** zoom
      )
docs: Return the pixel resolution for a given mercator tile zoom and lattitude.
  
      Parameters
      ----------
      zoom: int
          Mercator zoom level
      lat: float, optional
          Latitude in decimal degree (default: 0)
      tilesize: int, optional
          Mercator tile size (default: 256).
  
      Returns
      -------
      Pixel resolution in meters