docs: def _getZoomLevelRange(self, resolution, unit='meters'):
          "Return lower and higher zoom level given a resolution"
          assert unit in ('meters', 'degrees')
          if unit == 'meters' and self.unit == 'degrees':
              resolution = resolution / self.metersPerUnit
          elif unit == 'degrees' and self.unit == 'meters':
              resolution = resolution * EPSG4326_METERS_PER_UNIT
          lo = 0
          hi = len(self.RESOLUTIONS)
          while lo < hi:
              mid = (lo + hi) // 2
              if resolution > self.RESOLUTIONS[mid]:
                  hi = mid
              else:
                  lo = mid + 1
          return lo, hi