code: def _get_bounds(self, layers):
          
          extent_query = ('SELECT ST_EXTENT(the_geom) AS the_geom '
                          'FROM ({query}) AS t{idx}\n')
          union_query = 'UNION ALL\n'.join(
              [extent_query.format(query=layer.orig_query, idx=idx)
               for idx, layer in enumerate(layers)
               if not layer.is_basemap])
  
          extent = self.sql_client.send(
              utils.minify_sql((
                  'SELECT',
                  '    ST_XMIN(ext) AS west,',
                  '    ST_YMIN(ext) AS south,',
                  '    ST_XMAX(ext) AS east,',
                  '    ST_YMAX(ext) AS north',
                  'FROM (',
                  '    SELECT ST_Extent(the_geom) AS ext',
                  '    FROM ({union_query}) AS _wrap1',
                  ') AS _wrap2',
              )).format(union_query=union_query),
              do_post=False)
  
          return extent['rows'][0]
docs: Return the bounds of all data layers involved in a cartoframes map.
  
          Args:
              layers (list): List of cartoframes layers. See `cartoframes.layers`
                  for all types.
  
          Returns:
              dict: Dictionary of northern, southern, eastern, and western bounds
                  of the superset of data layers. Keys are `north`, `south`,
                  `east`, and `west`. Units are in WGS84.