code: def _get_default_annual_spacing(nyears):
      
      if nyears < 11:
          (min_spacing, maj_spacing) = (1, 1)
      elif nyears < 20:
          (min_spacing, maj_spacing) = (1, 2)
      elif nyears < 50:
          (min_spacing, maj_spacing) = (1, 5)
      elif nyears < 100:
          (min_spacing, maj_spacing) = (5, 10)
      elif nyears < 200:
          (min_spacing, maj_spacing) = (5, 25)
      elif nyears < 600:
          (min_spacing, maj_spacing) = (10, 50)
      else:
          factor = nyears // 1000 + 1
          (min_spacing, maj_spacing) = (factor * 20, factor * 100)
      return (min_spacing, maj_spacing)
docs: Returns a default spacing between consecutive ticks for annual data.