def map(self, data, layout):
        """
        Assign a data points to panels

        Parameters
        ----------
        data : DataFrame
            Data for a layer
        layout : DataFrame
            As returned by self.compute_layout

        Returns
        -------
        data : DataFrame
            Data with all points mapped to the panels
            on which they will be plotted.
        """
        msg = "{} should implement this method."
        raise NotImplementedError(
            msg.format(self.__class.__name__))