def get_description_key(resolution):
  """Returns GVIZ description key for the specific resolution."""
  if resolution == 'days':
    # It permits Google Viz to properly list days instead of midnight every day.
    return {'key': ('date', 'Day')}
  elif resolution in ('hours', 'minutes'):
    return {'key': ('datetime', 'Time')}
  raise ValueError('Unexpected resolution')