code: def zoom_in(self, incr=1.0):
          
          level = self.zoom.calc_level(self.t_['scale'])
          self.zoom_to(level + incr)
docs: Zoom in a level.
          Also see :meth:`zoom_to`.
  
          Parameters
          ----------
          incr : float (optional, defaults to 1)
              The value to increase the zoom level